My 4 month old Blue Toto flapper has begun dissolving. I have soft water and do not use a bleach tablet.?

The flapper also began to shrink so that it doesn't cover the hole.|||typically it happens from cleaning chemicals your putting in the toilet tank, but since you say your not I would have to assume that perhaps although rare it may be a faulty flapper. go to your local plumbing supply store and replace it, very easy to do yourself, but get a original toto flapper not a knock off.|||You need to go the store and buy high quality flapper or ask a professional for help.|||more than likely faulty flapper. I've used soft water since 1958 and never have that kind of problem.