12-10-2011, 12:52 PM
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On the sponge: as someone mentioned, these filters push more water through than one might realize. The noise at the surface can be controlled a bit by where the outlet is positioned; about half above and half below the surface seems to be the quietest I find. But I don't worry about noise since my tanks are in a fishroom. In a bedroom it would bother me I'm sure. I posted some photos of my two Elites in post #12 of this thread: Another Sponge Filter Setup Question
On the corys, if it is rapid respiration it is not likely to be oxygen shortage with so many plants. But before umping to issues, it may be normal. Corys that are moving around and feeding will naturally respire faster than after they have been sitting still for some time. Whenever I have had problems, the faster respiration is also belaboured, the gill covers are being pushed out far in an effort to pull in more water. And the fish are lethargic rather than active normally. If you do post a video I may be able to ascertain if there is a problem or not.