A sump is basically another tank under the main tank that provides a place to put all the equip such as heater, skimmer, carbon bag, ect... A wet/dry can be a sump. A wet/dry is a filter that uses bio media (bioballs, cellpore, plastic shavings, ect..) to remove ammonia/nitrite. It can be incorporated into the sump design or hang on the back of the tank. Read this for more info on sumps in general: http://www.aquariumadvice.com/viewtopic.php?t=20
In a typical SW
tank, be it reef or FOwLR
(fish only with live rock), a sump is used to house epuip and to provide a) water flow to the main tank b) increase the total water capacity. The current trend, and it seems to work very well, is to have about 1 1/2 lbs of LR
per gallon and a sand bed that is at least 4" deep. The live rock holds the bacteria to remove the ammonia/nitrite and, to a lesser degree, nitrates. The sand bed (DSB
) has the bacteria to remove nitrates. This is accomplished because the lower area of the DSB
has very little oxygen or is hypoxic. The bacteria that live in this environment feed on the nitrate. The problem with wet/dry's is that they are so efficient at converting ammonia that the system often quickly builds up an excess of nitrate. Please don't hesitate to ask any other questions you might have about this. We will help in any way possible.