Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
In my case, fresh water for the dogs.
1) Larger volume of water in the system.
2) Can keep a lot of equipment in the sump that would otherwise be in the tank.
3) Possibly better arrangement of filter media, and larger volume of media.
4) Easy to take water for testing, and add chemicals to the water. The additives (fertilizer, dechlor... ) get pretty well diluted before they get into the tank.
5) Water level in the aquarium stays the same. The evaporation is noticed by less volume in the sump. With the water level staying up high in the tank there is no mineral build up where you can see it. (The rim of the tank hides it)
6) The sump can be planted as a refugium. House plants grow well in a setting like that, if you can give them the light they need. Great filtration!