I'm having a problem! I have a 29 bowfront. My boyfriend sunk lava rocks into fiber glass all along the back, so the entire back is lava rock. This was his tank for years, and was out of use for a few months before he gave it to me. He did have some kind of infestation of parasites, white ovals that swam around, and all his fish died. But he pretty much boiled the tank for days and then it sat empty for months. It has undergravel filtration.
There are bugs all over the lava rocks. The bugs don't swim or go in the water, just stay on the few inches of rock above the water. (Because of how he made it I can't fill it up all the way or fish will get trapped behind the rocks, that's why there's so much extra space at the top.)
They look like fleas a bit. I don't think they fly, just crawl around. They're not on the outside of the tank at all. When I do top off the water as much as I can, some get in the water and hop on the surface. They are a brown gray color. I do NOT do well with bugs and feel like I can't even maintain this tank now. I have nightmares about this tank--I guess we all have our silly phobias.
Anyway, here is a link to a video of the bugs. http://youtu.be/9WskBjNCsfo
It was hard to get close enough to see, I know it's grainy but maybe you can tell what's going on. You can see some sludge they're making. I took the video right after I put more water in, to stir them up a little.
Thanks so much, I hope you can help! Honestly I'd really like to get rid of this tank! I feel like the lava rock is just too porous and will always harbor something. But I don't feel like I can just get rid of these fish in case I give someone else these bugs.