I've been using 130 1:1 and re-using the stock solution for months, and it's working great, much easier than mixing up developer and throwing it out after each session. I'm curious as to how to tell when the solution is exhausting. Will the blacks just get weak? Would it be better to keep track of the number of prints I run through it? PF states 50 8x10 prints per liter, is this optimistic?