Marine systems of whatever type, reef aquarium or fish only aquarium, can function successfully on their own without a sump, provided they are properly supported by equipment, are not overstocked and ongoing routine maintenance is completed. There is a way to enhance the seawater quality in the aquarium even if all the necessary guidelines have been followed religiously and that is to have a sump.
An aquarium sump is to all intents and purposes another aquarium attached to the main display. Seawater is pumped up from the sump to the display aquarium and flows down again by gravity, usually by the use of an overflow pipe. This flow is easily achieved.
All that is needed is to measure the available space for the sump – it could be inside the cabinet cupboard if there is one, in a separate housing alongside but below the main aquarium, or even in an adjoining room. Generally the bigger it is the better. Once the available space has been measured the aquarist can purchase a suitable aquarium. There will need to be at least two dividers in the sump, the first one is to accept incoming seawater and the last one is to create an area for the return pump. Some aquarists have more dividers for their own reasons, but two serve the basic purpose. The glass for these dividers does not need to be thick as there is supporting seawater on both sides. There isn’t any chance of a leak once they are siliconed in place as all joints are inside an already watertight unit. The finished job does not need to be perfect as it is in the sump and not on display. Measuring and siliconing the glass is a simple job, there needs to be an overflow at the top of each divider which is created by making the top of the dividers around ½ inch lower than the seawater level. If the aquarist doesn’t fancy the job then a local marine pet store will often do the job for not much money, especially if the needed aquarium has been purchased from the same shop.
The question of drilling the display aquarium for an overflow to feed the sump is one that puts many DIYers off. Again, the local marine shop will often do the job, or if not a local plumber often will. Alternatively, an overflow device can be used. These fit on the edge of the aquarium and seawater overflows by siphon. These units are available commercially, but do project above the top of the main aquarium to an extent so space needs to be available.
The first advantage in having a sump is that the system seawater gallonage has been increased. This means that seawater quality will be enhanced as there are more gallons per fish. Note that the extra gallonage created is not a reason to increase fish stocks as this would negate the advantage and also possibly create space problems in the main aquarium. There will also be an increase in the amount of seawater used for the routine seawater change; this is not a problem as generally the sump isn’t that large.
So what else could the sump be useful for? Again with a view to high quality seawater a deep sand bed (DSB) could be placed between the two dividers. The depth of the DSB usually starts at 4″ and many aquarists have them deeper than this. Note that ordinary coarse coral sand is not used as it needs to be fine sand. There is an article on DSB construction on the Aquarists Online website. Another way to achieve the same thing would be to install a plenum, which is a raised DSB. I believe most aquarists use a standard DSB. The aquarist should see many tiny life forms inhabiting the DSB which generally widens interest in the aquarium system.
The macro algae Caulerpa could be used in the sump. Again this algae is used for filtration as it feeds on nitrate and phosphate. Once established it needs to be harvested from time to time. The aquarist will need to provide lighting. This is not expensive to purchase or run as fluorescent tubes (T5’s or T8’s) fitted with reflectors are sufficient, usually two are positioned along the length of the sump. An electric timer is also needed if the aquarist is to run the lighting on a cycle. If so, it is advantageous to have the sump lights on when the main aquarium lights are off. The reason for this is that it helps stabilize pH.
Additional live rock could be placed in the sump (but not on top of a DSB as it would cause compaction). This increases the bio-filtration should this be needed and at the same time creates a new mini-world for the aquarist.
If the aquarist has a problem with a fish then, if the fish is not too large, it could go into the sump. This is not for treatment (if treatment cannot be done in the display aquarium then it cannot be done in the sump as the two are connected), but to give the fish some respite if it is being harassed excessively. Likewise, there is a place for any unwelcome hitchhiker that has arrived with live rock – for example, a mantis shrimp is not welcome in the main display aquarium but it could be transferred to the sump and become a point of interest.
Another practical advantage to the sump is that it can be the home for technical equipment that would otherwise be in the display aquarium. Heaters and a protein skimmer for example – the equipment is out of the display aquarium which benefits by the removal of unnatural items.
If the aquarist has room for a sump then it is very worthwhile adding one.