I think it is a nitrifying bacteria. It feeds on the nutrients in the tank. I have it as I write this post, on the roots and base of my plants. Small amounts here and there don't seem to be a problem for me. But it it grows to cover the roots and leaves it will 'suffocate' the plant. I clean it off every time I do a water change with a toothbrush or my fingers so it will be sucked up by a filter. I use a diatom filter at least once a month, and that really keeps many bacteria and parasites in check. If you have HOB filters, you can usually see it on the filter media as well....which is where it really belongs. If your water does not have much movement, or lacks a filter, you will see it more often covering things in the tank and on the surface as 'biofilm'. I don't use filters on my tanks, except the diatom filter monthly, so I see it often. Just clean the plants off and they will be fine.
