Drilling Holes for Bulkheads in Glass Aquarium Tanks

Drilling a tank is something that may make you nervous. Even if you see it demonstrated, you might not think you can do it. It is easy and fairly quick.


Drill bits for glass are called diamond hole saw bits. They don’t work quite the same way as a wood hole saw bit.

With wood, you pushing the drill and bit down hard is how the hole is made — you can go as fast as you want. Not so with glass.

With a glass hole drilling bit, diamond particles fused to the metal scratch their way through and wear through the pane gradually. It doesn’t matter what direction the bit rotates.

Using hard pressure to push down on the bit will result in the hole chipping out or worse, ruining the tank by cracking it.

If you haven’t drilled an actual tank, you may want to get some scrap glass at roughly the same thickness as what your tank is in order to practice. Rule #1 is take your time and let the bit do the work.

Aside from practicing the technique of drilling, care needs to be put into the bit you are using. Many cheap diamond bits will get significantly duller after only a few holes.

So make sure your bit is relatively sharp and new. You might want to get one specifically to practice with, then use a new bit to drill the hole on your tank. A dull bit takes longer to make the hole which may tempt you to push harder. Pushing harder increases the chance of chip out or cracking the tank.

Hole placement

Holes need to be a sufficient distance from the edge of a pane of glass in order to retain the structural integrity of the tank. The diameter of the hole is the measurement that determines this. From the edge of the glass to the edge of the hole, there should be at least the diameter of the hole in distance. From the center of the hole, it works out to 1.5X diameter. Holes in proximity should be 2X diameter apart on center.

Plumbing parts are supposed to be standardized, but you will find small differences. It’s best to get your plumbing parts and bulkheads prior to doing any drilling.

Glass Strength and Lateral Forces from Plumbing

Bulkheads and plumbing affect how the tank distributes force. A rigid bulkhead and length of pipe can act as a lever that will place forces on the glass. Once you install a bulkhead, make sure that you don’t let the tank rest with it’s weight on the bulkheads during storage or moving. – This is a universal rule for any drilled aquarium.

This is another reason why I like flex PVC so much, as it will give before putting excessive force on the glass. It won’t stress the tank if bumped by a child, dog or clumsy owner.

Glass Thickness

The number I tend to lean towards is 40 gallons for the minimum size of tank should be drilled. A 40 gal breeder (36″ X 18″ X 17″) has 1/4″ (6.35mm) glass which can withstand the forces of drilling and having plumbing hanging off it. Many stories of cracked tanks involve people drilling something under 40 gallons.

Tempered or Not Tempered

Tempered Glass is heat treated for strength and safety. If you attempt to drill it, it will shatter into many tiny pieces along with your perception of how intelligent you are.

On many standard tanks offered for sale that have rims on top, the bottom is tempered but the sides are not.

It’s fairly easy to find out if the tank is tempered with polarized sunglasses and a laptop with an LCD screen.

First, you want the screen mostly white – the easiest way is just to go to Google.com with the white background. Put the white screen device behind the pane in question and look at it while wearing the sunglasses.

Next, turn the device’s screen like a steering wheel – watch closely as it goes from white to black and then back to white.. If the screen is total black, the glass isn’t tempered. If you see streaks through the blackness, it’s tempered.

This page here goes over the process and has some helpful photos:
A good thread on Salt-City.org – How to tell if glass is tempered

Tempered glass can often have a couple of other telltale signs. For one, They will often be more rounded than your average piece of scrap non-tempered or plate glass. This is sometimes because a pane of glass will often have the edges rounded or polished before being tempered.

Also, you may be able to find a stamp in the corner that indicates that the pane has been tempered. These stamps can wear off, but may still have some ink on the glass. If you see these signs, the pane has a good chance of being tempered.

While non-tempered glass is easy to score and break, tempered glass is much stronger. They say up to 10 times as strong! This means it will not score as easily. Non-tempered glass has a distinctive sound it makes while being scored. If forced, (and it will take a lot of force) it will shatter LOUDLY. Not a good way to wake the house up!

Bit cooling

Cold running water over the cutting bit keeps it’s temperature down and carries dust away. The best thing you can do is use a hose on very low flow and direct it over the bit. Use freshwater. Take care not to get your power drill wet for obvious reasons.

Many demonstrations show drilling a hole in glass using a ring of putty or clay. The ring is fashioned around the hole to be drilled and then filled with water. This works, but doesn’t allow you to use a wood template to put the hole exactly where you want it. It also means you can only drill straight down which isn’t always possible.

If using a stream of water from a hose then the whole process becomes a little easier to view. this is because the water remains clear so you can see how far you have drilled through the pane.

Getting the hole started

First – make sure that your drill is correctly adjusted. If there is a clutch / torque setting – make sure it’s on the lowest setting. This is commonly adjusted with a collar ring just behind the drill chuck.

You may see some people angle the bit to about a 45° angle so that the entry angle focuses the bit force onto one spot. The cut starts to form a “C” shape and acts as a guide so the bit doesn’t skate around the surface of the glass before it can start.

I have found the angle-in technique a little difficult if you are looking to precisely put your hole where you want it. A thin piece of wood used as a guide works well. To make the guide, use an actual wood bit the same size as your diamond hole bit to make a hole in the wood piece. A thinner piece of wood is better because it will allow water to flow into the hole.

Now you can clamp the wood piece to your glass panel or get a helper to hold it while you drill. Once you get the hole started, you can remove the wood guide in order to get a better look at the bit and see how much longer it must travel you have before you make it all the way through the pane.

Drilling Technique for a Clean hole

For the best possible result, you should drill the hole from both sides. It may take slightly longer, but if your goal is to do it right and get a clean hole with no chip-out, then it is the best method.

First, start cutting through the pane, but stop cutting when about 75% of the way through. Then carefully line up and secure your wood hole template to the other side of the pane. Start drilling with light pressure until all the way through. It may take some time to line up the hole again on the other side.

If you are only able to drill from one side of the pane, technique and steadiness is more important to reduce chip out as the middle piece breaks free.

Towards the end of the cut you want to make sure that your pressure is soft, and let the bit carve the last way through. Excessive pressure at when you are almost all the way through can chip out the hole.

Changes in the angle of the bit can also result in chipping. You must put effort info holding your angle steady for the last few millimeters of the cut. If you feel yourself getting tired or shaky then take a break and come back to finishing the last few millimeters.

Very small chips on the edge of the finished hole are generally okay, but a significant chip can compromise the seal of a bulkhead.

Don’t let the Puck Drop

The circular puck of glass you remove can be something you want to account for, as it can potentially chip the tank where it falls. Take care to catch the puck with a towel or secure it with tape prior to drilling all the way through. Taping the opposite side of the pane prior to drilling may also result in less chipping and a cleaner hole if only making the hole from one side.

Drilling a tank that is full — A good idea?

This is a decision you’ll have to make yourself, but there are people who have done it successfully. If you know you can make holes cleanly without chipping then it may be worth the risk, just do to the fact that draining a reef tank is a major chore. It will still be more work than drilling a dry tank, but its doable if you want to put a hole in the side of the tank.

You would want to drain the tank by enough so that the drilling is not affected by the water pressure. It may be tricky to collect the bit cooling water in such a way that it wont leak into the tank. It is milky and full of glass dust your tank inhabitants probably don’t want.

If drilling a full tank, one challenge you may run into is how to orient the drill. To prevent getting glass fines in the tank, you will want to drill from the outside. If the tank is too close to the wall, you can’t get your drill in in the right spot to make the hole. You may want to find a “close quarters” drill. These allow a hole to be drilled in a tank with only about 6″ between it and the wall.

If you have no choice but to drill from the inside, you may be able to creatively catch the drilling water before it gets in the main tank water. Some ideas are a half-bowl or container pressed onto the glass, or a shop vac fitting duct taped under the hole to vacuum all the water. You’ll most likely need a helper for this. If you come up with a solution for this, please email me a picture.

Even if you have a lot of experience drilling clean holes, there is always the chance of cracking the tank. You may just want to prepare for this with several containers to hold your livestock and rock if the worst was to happen.

Reef Aquarium Sump Tank Design

Reef Aquarium Sumps are something that can be very simple and easy to set up if you know a few things about what you are trying to do.

A big reason why sumps are confusing to beginners is that a lot of people make them way more complicated than they need to be. They see all kinds of pipes going all over the place and think they must be hard to build.

Depending on the stand or cabinet you are using, it can be a hassle to remove or change your sump setup. It is worth putting some thought into how you are going to use it and what it needs to do.

Sumps are simple, and you can turn a $20 Craigslist tank into one that functions just as well as $300 commercial models. This article will go over what I think is the simplest method to set up a sump in a bare tank, with all the reasons behind the design.

What are the main benefits of running a sump?

  • act as a buffer-zone where water moves to be filtered mechanically and chemically
  • slowly process water in such a way that promotes stability of the water and avoids spikes in water chemistry and temperature
  • let you run equipment out of view, so you can have a clutter-free display
  • contain any leaks from equipment or reactors from reaching the cabinet or floor

What we’re trying to do here

  • catch the water from the overflow drain outlet
  • deliver water to the equipment that processes it
  • remove any microbubbles that may have been generated by the equipment
  • return the water to the aquarium as quietly as possible

But we also want to make sure we:

  • have enough room to deal with back-siphoned water when the return pump turns off
  • have fail-safes in place where possible to prevent floods
  • cooperate with the Herbie, Bean or “siphon-based” overflow designs

reef tank sump design

Size Considerations

Most of the time, you’ll want to have as big of a sump as you can fit in the area. While you may have heard about “added stability” with a larger water volume, this is usually not a noticeable thing.

Having a larger sump just makes a few things easier and less complicated. A bit of extra room to work with means being able to run just about any equipment you want. It’s nice to have some space available for extra live rock, reactors, and those sort of things.

The 3-chamber design shown in this article will work for the majority of larger sumps. If a small tank must be used – say 10-20 gallons – then you will probably have to alter the design and not use the center chamber. With a small sump, a 2-chamber design will allow the return pump chamber to hold enough water.

How much turnover should we have?

There are not many benefits to running high rates of turnover through your sump, other than having more water pass through mechanical filtration. Each individual piece of equipment processes water at it’s own rate, but most can process a very small amount at a time. For that reason I generally recommend a rate around 5X-7X of the display volume per hour. More on turnover rate here: What is the right turnover rate for a reef tank?

1st Stage – Where water from the overflow drains into the sump

The first chamber will have the highest water level and then cascade down to the other ones. For the first divider, you want the water to pass over a weir of some kind.

The reason for having water go over a wier is to maintain a consistent water level in the first chamber.

A consistent water level is something we need for the skimmer to work problem-free, and it’s also helpful if you have a siphon-based overflow. In order for the siphon to start, the outlet of the pipe must be submerged, but only by about 1″ (3cm) below the water surface. A siphon can’t start correctly otherwise.

Designing for your Skimmer

Most new skimmers available are non-recirculating models that operate in-sump. They usually have a recommended water height from the manufacturer they are designed to work at. This is usually at between 7-12 inches of water…

When a skimmer is dialed-in and properly adjusted, it’s pretty touchy. If the surrounding water level in the chamber rises, it reacts by overflowing the collection cup and skimmate collector. Not fun to clean up.

If you design this chamber to have all the water flow to the next one by passing over a weir, this won’t happen.

So if you are trying to figure out how tall to make the divider between this first chamber and the next, you may want to choose something close to 12″. You can boost a skimmer up to the right height with a DIY stand of some kind, but you can’t lower it if it’s already too high…

Having ample water depth in the first chamber gives you options. It allows you to change or upgrade your skimmer, just by adjusting the height of the platform.

Dealing with Back-Siphoning

When the return pump is turned off, gravity will cause the water currently being pumped up to the tank to fall back down. This means the sump will start filling up a bit.

The water comes from a few places. First, the water in the display tank will flow back through the return. Second, the water inside the overflow will drain. Lastly, some water from inside the pipes will drain down.

When added together, this can add up to several gallons of water flowing down to the sump.

There are ways to reduce this amount of water by correctly designing your Return Line and Overflow System, but no matter what – there will always be some back-siphoning of water.

This is why it’s nice to have a bit of elbow room when it comes to your sump’s capacity.

Ways to Minimize Drainage

Before we even get to planning out the layout of the sump, it is beneficial to reduce the amount of water that back-siphons and drains into it.

This is done by:

  • Return line outlet only submerged the minimum amount below the surface of the display tank.
  • Correct height of standpipes in overflow box – water will drain to level of lowest inlet in the box when the return pump shuts off.

Stage 2 – Housing Equipment (Optional)

The middle chamber of the design can have many uses. This can be an area for reactors, heaters, or anything else. Hanging lighting over the area for a frag rack or refugium area is also common. You will most likely want a constant water level in this chamber too. This avoids the risk of having pumps or heaters running dry from a low water level.

Return Pump Chamber – Where the water level fluctuates

Your return pump goes in the last stage of your sump, how ever many chambers that ends up being. The water level here will lower as water evaporates, and raise when you top off the system with fresh water. So some people will mark the glass to show what the water level is supposed to be at when the system is topped off.

A piece of masking tape to indicate the high water mark can be helpful. Make sure that when you mark this point, the return pump has been shut off and all water has collected in the sump from the overflow and return line… That is the true high point.

Making sure the sump doesn’t overflow

By designing the sump to have water flow over a series of weirs, we control where the the water level will change. As it falls from chamber to chamber, it will collect at the end. This last chamber’s water level will vary based on evaporation or top-offs.

So this means all the other chambers up the river (the ones where water passes over a weir) will remain consistent.

A cause of frustration among first-time sump builders is overfilling. It is often not discovered until the plumbing is done and the return pump is turned on, then turned off.

It can be tempting to make your return pump chamber very small, because that is probably the only piece of equipment that is going in there. Might as well make lots of room for the other chambers, right?

This can have unintended consequences, which I’ll explain.

When the return pump shuts off, gravity takes over. Water will start to drain from the overflow box, display tank, and inside the plumbing. All this water collects in the return pump chamber. If it can’t handle the volume, the water will fill the other chambers upriver. This can result in the skimmer overflowing or in the worst case the whole sump.

Overfilling when the return pump is shut off is the result of a simple problem — The chamber where it resides is too small.

Contrary to many sumps you have seen, the return pump chamber will often be the largest chamber in the sump.

The good news is that overfilling due to back-siphoning is easy to avoid. By calculating the return pump chamber volume beforehand, we can estimate how big it needs to be in the planning stage.

Determining Return Pump Chamber Size

First, we know that the return pump rests on the bottom of the sump.

It’s meant to be fully submerged, so we need at least the height of the pump itself as a minimum water level.

As the water evaporates from the system, the water level falls in this chamber. So at a certain point, the water level will get low enough that air starts to get sucked in.

If this happens, a loud slurping sound will be heard.

The typical pump won’t slurp air unless the water level is very near the inlet. So you need 2-3″ of water above it to prevent this from happening.

Figuring out how much water needs to be in there to keep from sucking in air gives you a baseline. This baseline will be where you can start measuring the volume of the extra capacity needed for drainage. This baseline water level will be also be close to the normal operating level of the chamber — while the return pump is on.

For example, in this case we will say that 6″ of water is the minimum water level that a return pump can operate without it starting to suck in air.

Above the 6″ mark will be the base of our needed “extra capacity.”

sump drainage capacity

Calculating Extra Capacity or for when the return pump is shut off and the system comes to rest

There will be a few gallons of water that drains down from these sources:

  1. Overflow box (drains to lowest inlet or standpipe)
  2. Display tank – the amount of water between the height of bottom of overflow weir and the height of the lowest point of the return outlet (usually only about 1/2″ of depth if you design it right)
  3. Inside the pipes (not much water unless using long runs of pipe)

So by adding these three sources together, we calculate the extra capacity needed when the pump shuts off. In the case of the overflow box and display water, the volume is easily calculated with L X W X H.

When the extra capacity is added to the minimum, we find out the total required capacity of the return pump chamber.


Even if you decide to forgo these calculations and just use a check valve, there is another issue with creating a return pump chamber that’s too tiny. There will be a lot of swing in the water level height. This means that the water level in that chamber will rapidly go down as water evaporates from the system, and rapidly rise when the return pump is shut off and water empties from the pipes…

So why does this matter?

Well if you are using an ATO (and you should for many reasons), then you will want it to top up the system a few times per day, but no more than that. If the chamber’s volume is too small, then the ATO’s sensor will trip constantly — possibly shortening the unit or pump’s life from overuse.

For this reason you might want to make your return pump chamber larger, just to avoid this excessive swing in water level height.

Teeing Off the flow of the Return

Some people will use their return pump to also feed the refugium or one or more reactors. This means they they Tee off the return line and direct some of the flow over to that equipment.

A downside to Teeing off the return to feed either a skimmer or a reactor is that it will affect the return rate up to the display.

The return rate affects the overflow. If you have a siphon-based overflow like a Herbie or Bean Overflow, then variations in flow will mean re-adjusting the valve. This can be annoying to have to do all the time.

These variations in small amounts of flow is one reason why the Bean Overflow design has an advantage over a Herbie design. The Bean has the ability to take on variances in the rate of flow through it’s open channel, where the Herbie would need to have the valve adjusted.

So if you’ve got a siphon-based overflow, the system works best if the return pump’s only job is to push water up to the display. The flow may be Tee’d off to provide flow to something that provides consistent pressure such as a refugium chamber, however diverting flow to a manifold to power media reactors generally doesn’t work well with a siphon based drain. This is personal preference because most people don’t want to deal with frequent adjustments.

Sump Construction

caulking gun

The dividers of a sump are called Baffles — vertical panels siliconed in place. The configuration of the baffles determines how the water flows from chamber to chamber.

In a glass sump, you should use glass baffles. Using silicone to affix acrylic panels to glass doesn’t work well in general as it will never create the same strong permanent bond as silicone to glass.

Dealing with Microbubbles

Tiny bubbles in the water are called “Microbubbles” and will blow around in the current of the water column, until eventually bursting at the surface. While they are harmless, they can detract from the crystal-clear look of the water. Common sources can be skimmers and overflow pipes, or anywhere water falls more than a few inches.

Bubble Traps are a series of 3 baffles placed one after another to ensure all the tiny bubbles dissipate. They work by moving the water vertically up and over a barrier where water is calm.

While they work well, they can take up a lot of room in the sump. If you don’t have a lot of room to work with, you might want to skip using a bubble trap. Most newer skimmers don’t produce many microbubbles at all, especially once broken in. Placing the skimmer near the drain line outlets on the opposite end of the return pump should create enough distance in order the for bubbles to pop before they make their way to the display. While not needed in every circumstance, it’s nice to have a bubble trap in place just in case you need it one day.

Building a Bubble Trap


Bubble traps are usually placed at the last divider before the return pump chamber. This way bubbles dissipate before getting pumped back up to the display tank.

Distance Between Baffles

As a general rule, the baffles in a bubble trap should never be closer than 1″ (3cm) to one another.

If you are passing water underneath a baffle, the panel should be raised off the glass the same distance. The height of the opening should be at least equal to the gap between individual baffles. This will avoid a bottleneck in flow.

While it may be the norm to only have 1 inch of space between baffles, it is really the bare minimum.

A gap of only 1" creates an area that is hard to access. A larger opening will be easier to clean between the panels. Furthermore, if you keep livestock in the sump, it can be a real pain to net something out from between 2 baffles if they are only 1" apart.

A gap size of 2" is often better, not to mention easier to install in the construction phase. By creating more space between the baffles, you promote stillness in the water. Stillness helps bubbles rise to the surface.

Under or Over?

The diagrams on this page show Under-Over-Under. Designing a bubble trap with this pattern is less common. There is no wrong way, but I find the Under-Over-Under way has a few benefits.

If you make the bubble trap the opposite way – as Over-Under-Over, it creates an area that is hard to access.

Over time, some detritus will settle at the bottom of an Over-Under-Over bubble trap. Not a big deal to most people, but if you want to clean out that part, it can be difficult. The space at the bottom is almost impossible to access.

Also – if you keep fish in your sump from time to time as I sometimes do – Over-Under-Over bubble trap can be a pitfall. If a fish gets in the middle – you will have a hell of a time getting it out.

So under-over-under might be the best way, but it’s personal preference.

Either way of setting up a bubble trap will keep microbubbles away from the return pump. Ultimately, a slow rate of flow is the biggest factor in how well they work.

Installing Baffles in a Tank

There are many steps involved in selecting and preparing your glass baffles. This info has been split into it’s own post: Reef Tank Sumps: DIY and Construction

Things like measuring, cutting, glass thickness and prep work are shown. There are photos of a 40 breeder sump build with some helpful DIY techniques for working with glass and assembling the sump.

Refugiums and Sump Setups

Some people will install a refugium into their sump. While common, there are plenty of people that just do without them. The term itself has become a little generic. A “Fuge” often just refers to an area of the sump where there is lighting and stuff grows.

What is the Sump actually doing?

A repeated statement in reefkeeping information is that your refugium needs slow flow running through it. This is not true in all cases.

Some people will Tee off the return pump and divert a portion of the returned water to a “slow flow” chamber. Reducing flow like this is usually counter-productive if the refugium’s main job is to grow macroalgae.

Macroalgae grows the fastest with two things present. Good water flow (more oxygen) and lots of light in the proper spectrum. Reduced flow will just impede it’s growth.

So the question is, why bother Teeing the return line?

It is simple to just place the macroalgae in a sump chamber with consistent water height. Usually the macroalgae needs to be segregated or prevented from getting sucked into pumps. A plastic mesh divider or basket can be used in these cases.

Some refugiums are created as a habitat for microfauna and all the critters that live in the reef. These area are a true “refuge” and will usually have some kind of sandbed. Providing a safe place away from fish and predators will theoretically let them flourish and multiply. The ideal amount of flow for these types of refugium zones is a matter of debate and many people have tried to experiment with them but there isn’t really a consensus.

If you are building your first sump then you will probably get the most mileage out of trying your hand at growing macroalgae like Chaeto. A more complicated refugium setup can then be something you choose to experiment with or forgo altogether.

More advanced designs

In the diagram at the top of this article, I show water moving from one end of the tank to the other. The water cascades, flowing from chamber to chamber like a waterfall. Illustrating the concept this way is simply done to make the concept easy to explain and show.

This design is generally a good practice. When the dividers span the whole width of the tank (front to back), the water passes over a longer weir. Having water pass over a longer weir allows for slower flow that is quieter.

Sometimes you want to go a little further with your design. In order to maximize what the sump can do, having each divider span the full width of the tank isn’t always the answer. More creative and intricate sump designs are possible. Rather than just having rectangular pieces of glass, you can create openings for water to pass through.

Cutting notched panels with the corner cut out allows for the sump to do a lot more with the minimum amount of dividers. For an example of this check out the Reef Tank Sump DIY Construction post.

Containing Spills and Being Proactive

Having a large sump with fairly high walls allows you to have a bit more piece of mind.

Equipment such as reactors have the potential to come apart and leak. The pump that drives them will continue to go, and can put water where you don’t want it.

Reactors may also have flimsy barbed fittings and tubing, especially on the cheaper models. If one of these fittings blows out, you want the reactor in a place where the water will only spill into the sump and not anywhere else.

The same also goes for things like a Skimmer’s Skimmate Container. While common to be be located next to the sump, what is to happen if it overfills?

Anything with the potential to leak should ideally be located inside the walls of a sump or just above it. It can also be a good idea to install a water alarm in the cabinet.

There are many ways that a tank can potentially leak, which you should always be aware of. For this reason I have also written this post here: Common Causes of Flooding on Reef Tanks

What is the ideal Flow Rate of Turnover through the Sump?

Turnover rate through the sump is something that people often overshoot while designing their system. They often end up with a louder pump than needed.

It helps to know a bit about how a sump works and how equipment is affected by the turnover rate. This will help you to make the best decision about how much water needs to pass through your system.

The Purpose of a Sump

Many people coming into the hobby do so from the freshwater side of things. Take for example a freshwater cichlid tank with many fish. When you are dealing with a lot of fish and trying to keep the water clean, mechanical filtration does most of the work.  Moving a lot of water through the filtration media is better in that case.

Mechanical filtration is only one part of a typical reef sump, and is sometimes left out completely. Most of the equipment present is not affected by the turnover rate.

A sump on a reef tank acts more as a buffer-zone where water can move to a separate area, to be filtered and chemically processed. But it isn’t a matter of dirty water going in and clean water going back up to the tank. In reality, a skimmer or chemical filtration reactor will only process a fraction of the water that passes by it. The majority just moves right on past. So rushing a ton of water through the sump provides no benefit for the skimmer or reactors to work any better.

What is the optimal Turnover Rate?

The 10X rule and the reasoning behind it

One thing you still hear quite frequently is that you need 10X or more times your system’s volume every hour when choosing a return pump. (An example would be a 90G system = 900GPH).

While the 10X rule is a nice round number, a turnover rate of 5X-7X of system volume per hour is often more than enough.

The 10X number has been around a long time. It’s hard not to think that most of the people who came up with it were basing it on the equipment that was available a few years ago. Older impeller-style powerheads were much weaker and less efficient than the ones we have today. Many of these newer pumps now have wide flow, and wavemaking capabilities.

Using some of these new propeller-style pumps means you don’t have to rely on the return pump to create random flow in the tank.

With most of the flow coming from powerheads, you don’t have to do anything fancy with the return line. Doing things like splitting the return outlet between multiple outlets generally isn’t necessary and can actually result in less flow than a single line. Same goes for using loc-line fittings to point the jet inside the tank. All this fiddling and over-plumbing really does is restrict the return pump output.

If you are trying to select a pump that is quiet and well suited to the job, just use a single outlet. Large enough pipe will also help to maximize the output of your pump.

Why you might want less turnover

By having a lower rate of turnover through the sump, there are a few advantages like:

  • A smaller return pump can be used, which has a few advantages of it’s own. A smaller pump costs less to buy, and saves money in the long run by using less power. Not a bad idea for a device that runs 100% of the time. There is also a pretty big difference in both heat and noise between a 500GPH pump and a 900GPH one.
  • You can stay well within the capacity of the overflow. A lower rate of return will also skim off a thinner layer of water passing over the weir. This decreases the chance of fish or debris going through the overflow teeth and causing problems at the inlets / standpipes
  • When adding chemical additives or top-off water to the system, they will enter the display at a slower rate. This ensures changes to water chemistry don’t happen too fast. The theory is this is easier on the livestock. We’ll have to ask them if it makes much difference.

Surface Skimming, Agitation and how to decide on a turnover rate

The surface tension qualities of water mean that organics in the water are naturally drawn up to the top 1mm or so. This is one reason why it is so beneficial to drain water from an aquarium via an overflow. By allowing the surface to renew, you are helping to add oxygen to the water and remove waste through a natural process.

So having a good rate of turnover (more GPH through the return pump) will mean more water goes over the weir of the overflow every hour. So more stuff will make its way to the sump and skimmer. This “stuff” can be dissolved organics and solid particles in the water.

But how are you to know what "adequate surface skimming" really means? Well – it depends.

This is yet another area of reefkeeping that is up for contention. Most would agree that surface skimming is important, but it is hard to quantify. The difference in results between a coast-to-coast overflow and a conventional one are mostly anecdotal.

It would seem that surface renewal is important to an extent, but it’s importance is often overstated. Many overflows can provide decent surface skimming, provided the overflow teeth are designed right. Sometimes this can mean cutting out the existing teeth and replacing them.

The bottom line is you will find examples of successful tanks that have all types of overflows imaginable. Most of them can attribute success to good tank husbandry, not what the turnover rate is or how wide the overflow weir might be.