I have a layer of "foamy" bubbles on the suface of my tank?? is this a good thing or bad. It goes away for a couple of secs when I add food but then comes right back. It isn't a bubble nest cause I don't have a betta in my tank. I have red tail loaches, striata botia, angels, cories, ottos, neons, and guppies. All levels in tank are normal. just did a water change 3 days ago. does anyone know what it is???? or how to fix it???