A lot of water can give you D too, but you need water if you have D, it's confusing.. lol
Coming off the pred can cause your heart to race/legs to hurt I was told by my GI, but low potas can do it too and cause the D.
Pred also eats potas from your system, it could've been the cause of it.
I have very low potas and am on Apo-K 600mg x 4 a day to help. Ask your doc for it if you got low potas, it's not expensive if you don't have coverage.
It's around $15 for the month I think (can't remember what my pharm said if I didn't have coverage, sorry)