I'm looking for ideas about a problem that has emerged recently. I have a 5000 liter water system flowing through my tanks. Stocking levels are low, and water changes are done with rain water; so the tanks are soft and slightly acid, but only mildly so. My plants and fish grew like mad for about a year, and I also had a lot of very small snails. Then, suddenly, about three months ago the fish and plants stopped growing and the snails died. Needless to say that the fish which had been reproducing in the system, Swordtails, Platies, Kribs, and Angels all stopped breeding. Any ideas about what I should look for... or how to look for it? I'm guessing it's either some toxin, or a mineral deficiency (Calcium?).