Pond snails, most likely. They are so small on plants.
If the plants are healthy, regular untreated tap water might kill them (chlorine, if your pipes are treated like ours) To get them out of your tank, drop in some lettuce (it will float) and they will get on it to eat. Lettuce is their favorite! Then remove the lettuce and the snails. Might have to do this a few times to get them all.
Pond snails are actually beneficial to the tank but I can't say much because I refuse to put them in my tank because they breed so fast.
Hopefully there are no egg sacs on the leaves of the plants. When I had my driftwood in with my pond snails the egg sacs were literally impervious to everything, I soaked it in hot water then left it outside on my doorstep for a bout a week in the summer then took it back inside and the sacs were re-saturated with water. I couldn't believe it! I boiled the driftwood then for about 20 minutes and scraped them off individually. Those suckers are impossible. The tap water doesn't affect the egg sacs, which is why a lot of people quarentine their new plants outside the tank for a week or so to make sure.
SO, good luck! Hopefully you catch them befire they become a problem but you can keep a population down by starving them. Pond snails prefer to reproduce when they have a lot of food. Pond snails will eat dying plant matter, keeping your tank in good shape though.
*ETA* I should add not to add chlorinated water to your tank. If you feel you must remove the plants and douse them in tap water then do that. The snails have established themselves in the tank though so that might not be beneficial. Just don't add salt to the tank!! It will harm the plants.
Last edited by Laki; 09-26-2012 at 06:02 AM.