Most likely there is Ich in your main tank. The only way to eliminate Ich from you tank is to remove all of your fish for at least 4 weeks.
I'm currently 3 weeks without fish in my display, I've learned the hard way to QT fish before introducing theem into my main tank.
Can you tell the difference between silica sand and argonite based sand by looking at it? I have found some whitish play sand that is not labeled either silica or argonite. I know some silica based sands are brown, but can they be white too?
I have a bunch of small (3mm) critters running around in my tank. They are opaque with a brighter head. They appear to have antenna and about 8 legs. These critters are swimming and crwaling on my plants (which have been in the tank for several months) and crawling into my substrate (crushed...