I have a 29 setup that is filtered at present time by an AC 110, it has 11 pygmy cory and aprox. 8 cherry shrimp, I have had the tank cycled for over a year but have only had these fish in it for 2 months. I am wanting to replace the filter with another one, I was thinking of a sponge filter (perferrably just one) but I was wondering if I went down to an AC 50 filter if this would be large enough to keep the tank cycled and good. I am trying to breed the cory's, the shrimp are doing fine on there own---I'm going to use the present filter on my other 55 gallon tank here shortly but I just wanted to know if there are any recommendations on the best or a better filter for this tank. The present AC 110 has a sponge over the intake (taken from an old AC 70) to decrease the intake but the outflow is still pretty heavy. THANKS