Originally Posted by callistra
The plastic bag might block too much flow... does it have holes in it or something or just solid plastic? That's how all the water gets into your filter.. You want something porous that the water can pass through but your betta can't. Putting a sponge over the outflow is fine.. I do that on mine too. Seems to work well.
We didn't leave it in there we just put a piece over it to make sure it didn't suck it up. We figured if it sucked up the piece of plastic bag then it'd probably do the same to him, which thankfully it didn't.