Im unsure with my biowheels.. I have a 55g with biowheels and 1 that's been uncovered due to the kittens always getting on top and knocking the cover around.. so, Iv'e been leaving the cover off. I dont want them to knock the cover into the wheels and cause them to stop moving.. So, will it harm the wheels to be left uncoverd? Or can DUST get on them even though they move and mess up the bacteria?.. I dunno prolly dumb ?

I think it's okay, dust is probably falling on your water anyway and the wheels are constantly turning, it's not like anything will get caught on the wheel and "break it." ... Unless your cat continues to jump on it. ^_^;;

For me, the covers help reduce the splashy noise, but don't do much else.

I do not have the covers on many of my biowheel filters - for I have the tanks on the bottom of double stands and to pour water into the filter to prime it after a water change is nearly impossible - and I hate futzing around with the stupid lids back in the back when I do it!

There is no problem with dust. Dust is a part of life. It is fine. The only reason you might want to watch a bit carefully is that sometimes the wheel can toss droplets of water up and out of the top of the filter. When mine do that, the droplets inevitably land on my lights. I do not like mixing electricity and water.... so when that happens I make sure I keep the lid on.

Turning biowheels are very tempting to a kitten. I have had one delivered to me in bed at 2am by an over-acheiving hunter. Great - he managed to "kill" a biowheel....

I know that the biowheel, being in a place with loads of water and oxygen available to it, does hold a nice colony of beneficial bacteria. I keep them in the filter and working for me as much as I can.

kill a biowheel!! omg that made my day.. ok then.. I will remove all lids then i'd hate to lose spinning of the wheel and lose my cycle..