Just a leftfield sharing that I've lost 2 corys in recent weeks who got stuck in the air pipe element of sponge filters, hidden at the back of my tank. A year ago I also rescued one that I saw in time. When they do their Cory dance up and down arcing and surfing they seem to end up in there once in a blue moon. I can't be the only person with such dim corys? Maybe it's because I have the air running quite low and the bubbles aren't coming out in a thick enough stream to warn them off. I've added some sponge in there today so they can't fit in. I remember when they were juvies they loved to swim up a glass feeding pipe I had and everyone knows a Cory loves a gap to squeeze through. Anyway, I know it's an unusual post, but maybe it's worth mentioning. I've never heard of anyone else netting or blocking off their air filter.