Water Tank-Snails?

["Raymond O'Donohue" <rayo@cfw.com>]

I've thought about this,and have decided it would be a bad idea to 
put anything in there.As folks have pointed out,the snails are suspected 
of being agents of various ailments,and I suspect a goldfish from a  fish 
farm carries a few nasty things along when he arrives in the water 
tank.This tank is of course a small "system" without all the checks and 
balances of a creek,etc.And any fish must poop.So,unless there are other 
ideas out there,I'll just have to clean it more often,By the way,this 
thing has been a gem.It's a concrete item,about 30' high and 24'sq.Holds 
about 7 or 8 gallons,has a covered toilet- type float valve,and the 
adjustable heating element is set for about 48 degrees.Research has shown 
that horses may not always drink what they need from very cold water.