Reefkeeping Basics by Greg Taylor

Everything You Always Wanted to Know About Sumps, Part II

When writing Part I of this article, which described how sumps work and why sumps are such a popular part of reef aquariums, I didn't expect the subject to be quite so broad. My initial expectations were that one further article would complete my coverage of the topic. However, after compiling all the feedback from the first article and completing the research for the follow-up, I discovered that the information remaining to be covered couldn't be shoehorned into one article. The remaining articles in this series will progressively delve deeper into the design and concept of the sump and provide some techniques on how to avoid some of the common pitfalls when planning and assembling a system. If you have feedback or would like to see specific subjects covered in upcoming articles, please provide feedback in my author forum.

Although this series is far from an attempt at a comprehensive documentation on the subject, it would take a rather thick book to cover it properly. The intent of this series of articles is to provide a starting point and some basic "rules of thumb" to keep in mind in designing a system, or adding a sump to an existing aquarium.

When designing a sump for your aquarium, the size, shape, and material chosen should be carefully considered. While many of these parameters will be determined by the physical constraints of the installation, others will be determined by the expense you wish to incur.


The general rule of thumb for the "ideal" sump volume is "as big as possible." Of course, there are some realistic constraints that must be applied. Normally, those constraints are based on the size of the area in which the sump will be installed. I've also heard a rumor that not everyone puts every dollar they earn into their reef aquarium, so perhaps there may be monetary issues for some as well.

If a typical installation is planned that locates the sump under the aquarium stand, then the useable area under the stand will dictate how large the sump can be. When measuring the available space for a sump under the stand, don't forget to take into account any space that will be taken up by other equipment such as external pumps and chillers. Avoid squeezing too much into this area, if possible, as it's best to leave plenty of room to maneuver around the sump. Equipment that is difficult to work on leads to an avoidance of fixing minor problems and doing regular maintenance which, in turn, results in major problems or unnecessary equipment failures.

So, bigger does not necessarily mean better. While the rule of thumb above states to provide a sump that's "as big as possible," there are some other considerations to bear in mind. In the previous article I mentioned that there are many benefits to increasing the total water volume in the system. However, it must also be noted that there are some minor detriments to that concept as well. A larger water volume also means that larger or more powerful equipment must be provided, such as heaters, chillers, protein skimmers, and UV sterilizers, all of which may impact budget constraints on the project.

The most important consideration is that the sump must be large enough to handle the aquarium in question. There are two considerations in this regard. First, the sump must be able to handle the drainage from the aquarium when the pumps are shut off without overflowing. To view an animation of this, click here. For this reason, the sump will always be less than full when the pumps are running. Also, the sump must have enough water in it to provide the benefits described in the previous article, and to avoid problems such as noise and annoying bubbles. This handy online calculator can be used to determine the recommended volume of a sump that will be necessary to handle the overflow from a given sized aquarium.


Generally speaking, the shape isn't a critical factor, but there are some things to think about. The drain from the aquarium into the sump should always be located as far as possible from where the water is being removed from the sump and returned to the aquarium. This will maximize water exchange in the sump and help minimize the amount of bubbles that are returned to the tank.
There will be more to come on this subject in future installments. Choosing a "tall" sump is fine as long as access to equipment inside the sump is possible. For example, it's important to avoid a situation, where a skimmer can't be removed from the sump without dismantling the entire system and emptying the aquarium. So, as a general rule, it's best to maximize the dimensions of the sump to fit the available space while still allowing for proper access to the equipment.


Material choice could be the most difficult decision to make, since a sump can range from a custom-designed acrylic sump costing hundreds of dollars, to a $5 plastic storage container easily found at the local dollar store. Each has its own costs and benefits, which is what makes the decision so difficult. I'll briefly discuss each of them in no particular order.

Plastic Containers

Because I lean more towards the "thrifty" end of the spectrum than most, I have found success in a number of systems I've built by using plastic storage containers. As long as one can be found that is the appropriate size and shape and is made of "food grade" plastic, there will be little difference in performance between these containers and a more expensive off-the-shelf-type acrylic sump. When choosing to go this route, be sure to avoid any containers that have attached lids with metal hinges, as metals corrode, creating possibly toxic compounds being added to the aquarium over time. On some occasions I've been unable to find a container of suitable size and dimensions, but with an aquarium of less than 200 gallons, that's very rare. Although several trips may be necessary, sometimes going to every store in the neighborhood, one of them will probably have something that will work.

One very nice feature of choosing this option is that if a mistake is made during assembly and the sump is ruined, such as when the optimum bulkhead placement changes as little as a few inches, a replacement sump is cheap and easy. I've been known to buy at least two identical containers for a given project as advanced insurance for just such an occurrence. On one occasion I used a backup container used to store winter clothes for six months before I decided to re-plumb my system with a different configuration. Since it was the exact same container, it was a simple matter to swap it out, re-use most of the plumbing and only change out a few parts.

Another nice feature of using plastic containers is the ease of drilling for bulkheads (due to the thin walled plastic), which can be a real plus for a rookie sump installer. On the other hand, that same thin walled plastic that is so easy to cut holes in is also more likely to be damaged than more expensive alternatives.

Figure 2. A plastic container being used as sump. The bulkhead installation is clearly seen on the upper right side of the container. Photo courtesy of Cameron Coe.

Acrylic Sump or Wet / Dry Filter

Acrylic is a good choice for a sump because it is easy to drill, yet has high durability when reinforced properly and has a nice clean appearance. If the aquarist is handy, a customized sump can be assembled that will fit the available space like a glove (because it's built exactly to the size needed) and is relatively inexpensive. On the other hand, if the aquarist is not prepared to venture down the DIY sump road just yet, it's usually not too difficult to find someone that is experienced in working with acrylic that will build a sump, although it will likely be discovered that it is suddenly not such a cheap alternative. A more modest approach price-wise in the "acrylic sump" category would be a pre-built sump or wet / dry filter. With this option aquarists are at the mercy of "standard," pre-made sizes, but as long as a "standard" sized stand is used, it is probable that something appropriate can be found without a lot of hassle.

Wet / dry filters are nothing more than a sump with a built-in chamber within which bio-media is installed. If live rock or live sand is used as bio-filtration, then the bio-media is more of a detriment than a benefit and should be removed. To make a long story short and avoid getting too far off topic, wet / dry filters are excellent methods of dealing with ammonia and nitrite in a fish only system, but are not effective at processing nitrate which can be a real detriment to reef aquarium systems.

Acrylic is far and away the easiest material to modify in order to add chambers or baffles to the design. Some excellent tips for working with acrylic can be found in a previous Reefkeeping installment here. If you aren't sure why chambers and baffles would be needed, stay tuned. I'll get to that in a future installment.

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Figure 3. A well-built custom designed sump. An acrylic sump can be as simple as a box, but if you DIY extra features can be added with ease. Photo courtesy of Chuck Fiterman.

Glass Aquariums

In addition to using a standard glass aquarium for the main display, many people choose to use a standard aquarium as their sump as well. These are quite handy and, if done properly, can provide a very "clean" and simple installation. Depending on the situation, it can be a very cheap or very expensive alternative. For example, I use a 10-gallon "leader" tank as a sump for my 30-gallon reef. The cost was less than $10 and it fits perfectly in the stand. On the other hand, a friend uses a 110-gallon tank as a sump for his 300-gallon aquarium, but with the current retail cost for a 110-gallon aquarium over $300, this is not exactly an economical solution.

The difficulty involved in drilling a glass tank for a bulkhead is another factor to consider when choosing a glass sump. However, when using a submersible pump for circulation, as I do with my 30-gallon reef, drilling is not an issue. If a more powerful external pump is required, then the tank will have to be drilled. While drilling a glass tank is considerably more complicated than drilling plastic or acrylic, it can be done without a lot of effort if the correct equipment is used (diamond hole saw and drill press) and the aquarist has the nerves of steel needed for drilling fragile glass.

Figure 4. A standard 30 gallon aquarium in use as a sump.
Photo courtesy of Skip Attix.

Watering Troughs

Plastic watering troughs are generally used as sumps only for very large systems or where a "fish room" is available to hide the sump. There is simply no way to fit one of these under your tank stand. Bulkiness and poor aesthetics aside, they are an excellent way to provide a large sump to your system. Additionally, they are very easy to plumb. Most troughs come with a pre-installed bulkhead, although it is suggested that the low-quality stock bulkhead be replaced with a higher quality version to avoid unnecessary problems with leakage. Since they are designed to hold large quantities of water and usually have a large water surface area for beneficial gas exchange as well as providing plenty of extra room for supplemental equipment, they really make ideal sumps.

As with plastic containers, be advised that some of these containers have algaecides in them to prevent algae growth and these are best avoided. Although I've not seen any troughs in my area of Florida with this treatment, I've heard of them in other areas. Check to see if the label says "treated to prevent algal fouling" or if it contains an algaecide. They are often more expensive than the non-treated troughs, so the manufacturer is likely to point out this feature to explain the extra cost. If you see no mention of algaecide, then the container is most likely suitable.

Troughs can sometimes be found at the local hardware store, but are almost always available at a feed or tractor supply store. Price is variable depending on size, but is usually much lower than alternatives of equivalent volume.

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Figure 5. A watering trough in use as sump. It provides plenty of room for equipment and lot's of extra water volume.

As you can see there are many options with good reasons to choose each. Now it's up to you to apply them to your situation and make the best choice.

Stay tuned for the next installment of "Everything You Always Wanted to Know About Sumps, Part III" where I will cover drain hole size and placement as well as flood avoidance techniques.

Link to Part I & Part III

If you have any questions about this article, please visit my author forum on Reef Central.

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Everything You Always Wanted to Know About Sumps, Part II by Greg Taylor -