I have a Penguin 150 on a 30 gallon tank. This is not ideal, I know, and I want to add a second filter. The problem is that my fish are all about 2 inches/5 cm long and occasionally get tossed around near where the water returns when they're not paying attention. I think another filter would bother them. Should I wait until they grow bigger to improve the filtration? Is there a way to make the resulting current gentler, but keep the good aeration?