Lol yes I just cleaned that out, I had recently planted a few new plants, some of the dead leaves floated off and some of that liquidy silicon stuff they use to root plants in. Tanks been up about 2 1/2 monthsIt looks like the intake for your filters could use a cleaning. How long has your tank been set up and what are your parameters using liquid test kits? My 90 gal looks exactly like that right now and yes it is bacteria. My tank is still cycling though.