A couple of weeks ago I purchased a tank with fish from someone on Craigslist. I noticed that one of the mollies did this rocking motion. After hours of research I figured out that it was live bearers disease also called molly disease. I learned that it happens from a result of low calcium and electrolytes in the water. I found a bunch of chemicals that would fix it but most of the chemicals also harmed snails. The chemicals were also really expensive. So I found wonder shells. Really cheap! I spent $3 on the shell. I put it in my tank and 6 hours later the rocking that the molly had been doing for the 2 weeks that I had her stopped. Shes much more active. A few days later my water is clearer, fish are brighter, and my snails keep mating. The package actually said something about increased sexually activity in fishes. So this might be good for all the breeders as well. I also put in a shell with my bettas but I haven;t noticed a difference with them yet. Just thought I would pass it along. I have recieved some help on here and just wanted to pay it back.