I have 2 filters that are canisters, Hydor Pro 350 and Eheim 600 on my 75 gallon tank and they produce a bunch of micro bubbles, I have turned each one off for several hours in turns to see which one is causing it. Seems both of them are, I've even turned both off and used my Magnum H.O.T. 250 on it with the micron filter to try and get rid of them along with other particles after water changes and nothing happens. The tank still looks okayish, but it is very bothersome having the bubbles everywhere. I just changed all of the filters in the tanks and put in new filter floss in both of them, as it was time and even after 4 hours it is still the same. Any ideas?