Thinking about it, I am getting some calcium oxalate, but it is in the form of a precipitate in the water wash after the developer (that is cloudy after a print or so, I normally use a fresh water bath for each print).

However, I'm thinking that the calcium oxalate does not have the tendency to form structures large enough to be visibly crystal forms unless there is an extremely large amount of calcium in the wash water, because it appears to precipitate rapidly before it has the chance to collect into larger structures.

I'm thinking that it is a good suggestion for Mike to explore with some distilled H2O in the first bath, but it doesn't seem that it is the most likely candidate for the crystal problem.

It might also help if he reduces the PO concentration down to 20-25%, as that would also reduce the possibility if the oxalates are indeed forming a crystalline calcium oxalate.