check your water and go from there.
i run 4 cans (2x 2217's + 1x 2215 + 1x xp3) and 2x sponge on a 180g with 3x 12"-13" dats, 2x 6"-7" dats, 1x 10" bala, 1x 10" leporinus and 1x 10" bichir. i do 50% w/c weekly, with daily feeding. I will never remove my sponges as they saved me a couple of times when I forgot to turn on the system after a w/c on this very tank and my other 60g.