Why Not Have A Sump

Marine aquarists are always looking for ways to improve their systems. During the research and building stage, there may have been financial restrictions or other problems which no longer apply, which allows the aquarist to upgrade.

Perhaps a more efficient skimmer could be obtained, or some other piece of equipment. Maybe more live rock would be beneficial, so that the fish only aquarium could be fully stocked or in a reef aquarium the reef extended.

There is one item that is really useful, and that is a sump. Many, perhaps most aquarists have a sump as part of their system from the start. If there isn’t a sump, is it worth having? I would say a definite ‘yes’ – and it doesn’t cost a great deal either.

There isn’t any guideline for the size of a sump, it can be any size. However, the bigger the better, and the only constraint is fitting it.

What is a sump basically? It is a second aquarium to which seawater flows from the main aquarium and is then pumped back again. The first question is where can it go? Many sumps are fitted in the cupboard that is often below the display aquarium when that unit is supported by a stand. Space needs to be left above the sump so that servicing can be done, for example a protein skimmer needs cleaning and the collection cup lifts upwards. It isn’t necessary for it to be in that position though, it can be alongside the main aquarium and a little below it. It goes a little below it so that seawater will naturally flow by gravity from the display aquarium to the sump. The seawater is then pumped up again.

Having found the dimensions that can be used, the aquarist can either have a sump made or buy an aquarium off the shelf. There’s nothing special about a sump, it is simply as said a secondary aquarium.

One modification is required to run a basic sump, and that is to have a special area for the return pump. This is very easily accomplished by dividing off the end of the sump, leaving room for the pump to just comfortably fit in. The glass partition that is used has its top a little below the seawater surface, so that seawater flows over the top of the divider into the pump area. The pump used should be capable of moving the total system net gallonage around 3 times an hour. (Note that this is the seawater movement through the sump – the seawater movement in the display aquarium itself is more vigorous).

It has already been stated that the seawater gets from the display aquarium to the sump by gravity and is then pumped back through a tube connected to the return pump. How does it get out of the display aquarium? There are three basic ways to achieve this, first the overflow box, second by drilling the side or back of the aquarium, and third by drilling the bottom of the aquarium.

The overflow box can be obtained commercially. They are sometimes called a siphon box. They sit on the edge of the aquarium and seawater flows to the sump at the speed determined by the inflow from the sump. The overflow box must be able to handle the amount of seawater coming from the return pump These overflow boxes are more dependable nowadays, but problems can still occur if air gets into the box system. They are also noticeable as they protrude above the top level of the display aquarium.

The second is achieved by drilling a hole (or holes if two overflows are desired) through the glass at the side or back of the display aquarium. It is usually better to drill the side as there will be access problems at the back. Once the hole is drilled to a specific size, then a fitting and pipe are attached to allow seawater to overflow to the sump. The drilling can normally be carried out by a professional if desired, and can be done on a new or ’in use’ aquarium (the seawater level is lowered to allow the hole to be drilled).

The last way is achieved by drilling a hole in the bottom. This needs to be done when the aquarium is first purchased for obvious reasons. A fitting is placed in the hole with sealer and a vertical pipe attached, the top of the pipe is at seawater level. The seawater overflows down the pipe and is directed to the sump.

Out of all three basic ways of getting seawater to the sump, in my opinion the second option is the best. As said, an overflow box could have a problem if air finds its way into the pipe work. The third, the hole in the bottom, is usually fine but can be noisy as the seawater drops down the pipe. In addition, though unlikely, if a leak did develop then there is the potential to drain the whole aquarium to empty – not a happy thought! The second option, however, has the hole fairly high up the side of the aquarium – if a leak developed the seawater would only drain down to the hole level. Unlike the hole at the bottom, the hole on the side is accessible and repairable. Also, the pipe is outside the aquarium and doesn’t look ugly and out of place.

Using the second option, the professional will advise how high the hole needs to be – it cannot be too high or the glass is over-weakened. This leads to another question, and that is what of the seawater level? The seawater will find a level a little above the bottom of the overflow hole. The level can be easily adjusted by inserting a plastic elbow on the inside of the aquarium into the side fitting. It is not sealed (there cannot be a leak) and is left as a tight push fit. To obtain the correct seawater level, rotate the elbow a little as required. The seawater will overflow into the elbow and stay at the level selected.

The above may sound complicated but it isn’t. Drilling the glass is straightforward to a professional (many competent DIY aquarists do it themselves) and fitting the overflow pipe is easy.

So the sump is in position. What can be done with it? Many aquarists construct a deep sand bed (DSB) to assist with filtration. Some put a shallow decorative sand bed in, and use it to keep an interesting shrimp etc (just one or maybe two small ones, see the next paragraph). Some use it to grow the algae Caulerpa which assists with the removal of nitrate and phosphate. It can be used to house heaters and the protein skimmer, thus removing them from the display aquarium.

One thing the sump should not be used for is fish. The display aquarium should house fish if desired. The reason fish do not go into the sump is that this would negate, partially or fully, the advantage of the extra seawater gallonage the sump provides. The seawater in the sump adds to the gallonage that the fish in the display aquarium have available, therefore there are more ‘gallons to fish,’ which is advantageous to seawater quality. It means of course that the calculation for fish load should be made using the physical dimensions and net gallonage of the display aquarium only, the sump should not be included.

One final point. Once the sump is in position and the sand, rocks or whatever are in place, a check of overflow capacity should be made. If there were to be a power failure, then the return pump would stop and the seawater that had been pumped to the display aquarium would return by gravity, until the seawater level in the display aquarium reached the overflow level. This seawater entering the sump is additional to what would normally be present. To do a test, remove some seawater from the sump (keep the pump covered with seawater) and turn off the electricity supply to the return pump. The return pump stops and seawater runs to the sump from the display aquarium. Watch it rise and note when it stops. Either remove some seawater, or add some, so that the level is where you want it. This will be the level the seawater will reach if the electricity supply fails. (Note that when the return pump is running the seawater level in the display aquarium will always be the same.)

So if your looking for an improvement to your system, have you got a sump? If not, some serious consideration is worthwhile.


Why Not Have A Sump
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  1. looking for plumbing scheme for my aquarium

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