I have a 75-gallon tank with a 300 gph HOB
filter. Initially the high water turnover was good for filtration, but as I've added more and more plants it seems increasingly unnecessary. I've just added a CO2
system and I'd like to limit flow so as to keep more gas dissolved. I've raised the water level until it no longer splashes, but what I have now is a strong circular current at the surface. I'm also looking at a couple fish that dislike current and like to just float at the top, so I'm looking for a way to either reduce the flow or direct it downward again.
I have a similar problem in my feeder tank, which is a 5 gallon with 40 gph
filtration. I want to adapt that tank to house fairy shrimp, which are very weak swimmers.
I'm thinking about just sticking a sponge in the outflow, but I suspect I would just end up with a higher water level in the filter box and water overflowing the top of the sponge.
Any other ideas?