Nicole,
I do not use any product full strenght nor re-use it.
In the Xtol case, I use it 1+2 dilution so it is one shot.
I use Xtol since 1998 so I have a proven routine with it, and repeatable results.
I use boiled water for mixing stock and never saw such deposits, given that I did not move and the water company has not changed since 1998 in my town. I always use the same vessel (dedicated to mixing Xtol, and same glass bottle also dedicated to this product. So I'm puzzled by these deposits.
The HP5+ films came perfect, but I wonder what is the cause ad what are these deposits.
Anyway , thanks for your help !