Please help, is it parasites?

We have 2 little red snapper turtles in a 55 gallon tank. This tank previously had some fish in it from our local lake and we ended up getting what we thought were parasites. We cleaned the tank--clear down to bleaching the tank, bleaching the decorative rocks and other decorative items in tank. We threw away the rocks that were in the bottom in fear of not getting them clean enough. About a week after all of that we got some red snapper turtles. Put them in the tank(we got them July of this year) and haven't had any problems until recently. The turtles are thriving very well so we don't think the 'parasites' are harming them. The 'parasites' look like little white moving around. As I was reading another article I think that myabe we aren't cleaning the tank enough....the last time it was cleaned was the beginning of November. BUT we've been cleaning the tank once a month with no problems until now. Usually when we clean one tank we clean both of our 55 gallons. My husband has had fish ever since I've met him but this is our first time with turtles. PLEASE HELP US we don't want to loose our turtles--our kids would be devistated!