Where in the tank should I place my filter?
Is there a ‘best’ place to position an internal power filter with regards to water inlet and outlet, as well as flow? I can’t find a definitive answer.
HARRY FLETCHER, VIA EMAIL
NEALE SAYS: The usual position is to have the internal canister at one of the back corners of the tank, with the outlet pointing along the long axis of the tank. This will give active fish, like danios, the best opportunity to swim in a strong current. Ideally, the inlet would be close to the substate, so that it sucks water along the bottom of the tank, drawing solid wastes into the filter. At the same time, the outlet will be at or just below the surface, so that the surface water is agitated. This isn’t so much to mix air and water, but to increase the amount of water in contact with the air, speeding up the rate at which carbon dioxide and oxygen are exchanged at the surface. Bubbles, like those from airstones, do much the same thing — the idea they somehow force oxygen into the water is a common misconception.
In practice, it’s rarely the case that internal canister filters are ‘just the right size’ for a tank, such that the outlet is at the surface and the inlet just above the substrate. Of the two options, it’s probably best to prioritise the outflow, because keeping the water well oxygenated is so important. The compromise made, of course, is that with less ‘suction’ along the substrate, solid wastes are going to accumulate and become more unsightly over time.
Sometimes, you might need to direct the outlet towards the glass or a large vertical stone to spread out the water current. If you’re keeping slow-moving fish or amphibians that dislike strong currents, arranging the filter this way will ensure you keep the required turnover rate but don’t create currents that are so strong the fish struggle. On the other hand, some fish and invertebrates thoroughly enjoy strong currents. We’ve mentioned danios, but you’ll also find that fish like catfish and many shrimps, such as the Fan shrimps, spp. will actually arrange themselves to perch on logs or rocks pointing directlyinto strong currents. That mimics their natural behaviour in the wild, where they orient themselves into the current while feeding.
If you can get two filters, this will allow you to ensure one is sucking up water from the bottom of the tank, while the other is placed close to surface so the outflow ruffles the surface layer of water. Best of both worlds!
Atyopsis
Otocinclus