Hi!
are there perhaps problems of infection?
use green malachite in the water!
to this intention I have found this link that could serve you:
http://www.petsforum.com/novalek/kpd26.htm
With the green malachite, you perhaps resolve the problem
me for every change of water me use to add an abundant pinch of salt every 5 liters, and with my spiniferus I have never had problems.
For the fund of the little pond I believe is all right sand-blasts end for aquariums! But if is the first year, and if don't resolve the problem to the shell I dissuade you to put out her in the pond!
Resolve first the problem of infection!