Unknown infestation

Question
Rachel,
I have had my tank for several months with Mollies and a few Cories.  They have been pretty happy in the tank up until a few days ago when they started acting funny.  While looking a little closer I could see small particles floating in the water.
I thought this was uneaten food and didn't pay any attention.  Then I noticed what appeared to be air bubbles on the rocks within the tank, then noticed that the "air bubbles" would move around the rocks.  That's when I noticed that it wasn't food particles in the water, it was something "swimming" around the tank.  This caused me some concern since there were millions of them, on everything.
I read on the Internet that it could be Copepods which can result from a dirty tank.  I clean the tank about once a month since it seems that having live plants in the tank don't react well to the weekly cleaning.  So when I tried to vacuum out the little things I checked to make sure the tank was clean.  And it was.
I also read that it could be fish lice, but these hook onto the fish and cause an inflammation.  I haven't noticed this in any of the fish, although I just lost the two oldest males in the tank.
If this is Copepods, could you tell me how to get rid of them, or what I could get to keep them under control?

Answer
It does sound more like the copepods than lice as there would be signs on the fish. You did right by cleaning the gravel as this is the main dwelling of these little pests. Bottom line is that they are not harmful if they are just little copepods. If they are lice you will notice in behavior and appearance of the fish. Assuming they are copepods of some sort I suggest making sure the gravel was completely cleaned and cleaning the filter. Also, do not feed your fish for two or three days, they should have no problem surviving for this time without food if they are healthy. In fact, they should begin to eat the copepods. Once you resume feeding, only feed every other day for a week and then go to every day but only once a day. The copepods come from excess food and waste, if you cut down on the food the waste should also cut down leading to a cut down in the little guys. Never feed more than once a day. It may take a week or two of periotic cleaning and proper feeding for the little guys to lesson but with time they should. Also, fish like corys, platys, mollies, and angelfish like to eat these little guys. If you watch your tank closely I bet you will see one or more of the fish eat some of them. Follow the above directions and be sure not to overfeed. In one week, do another complete cleaning. If they do not leave by two weeks let me know and I will help you further. I hope this helps. Let me know if you need anything else.