water would definately help. I would also suggest a high quality granular PO4
sponge for a few days as well. It will help get rid of the remaining PO4
as well as picking up the silicates. Remember, water source is not the only place that these elements can be introduced. Foods are just as nasty at introducing PO4
(not silicates), meaty foods being the highest offenders.
Unfortunately the star may not recover. Once the deterioration starts, it rarely stops. Hopefully you will not have that happen but there is no way of correcting the problem. Drip acclimation
for inverts is always the best method and will greatly improve the odds of success when introducing them...