I prepare my PO solution just as Eric describes and I have never had crystallization problems, but then again I nearly always use the PO solution at room temperature.
However, if I understand the issues as they are being stated, I conclude the following. Please correct me if I am wrong.
1. Michael proposes using a weaker solution of potassium oxalate because this apparently gives better clearing in his condition. I am assuming he mixes the PO solution from well water rather than with distilled water?
2.Ole suggests that problems in clearing may be due to the formation of calcium oxalate, and proposes as the solution ether filtering the PO solution, or mixing it with distilled water, noting that reducing the concentrate of the PO solution will not address this particular problem.
3. Eric uses a concentrated solution of PO, and mixes with a reverse osmosis system, and apparently gets good clearing with this technique.
In my own work I usually have no problem at all in getting good clearing, with PO solution mixed with tap water, but have noticed that from time to time a fresh mixture of PO would immediately result in some staining, even though all other conditions were the same. From this discussion I am beginning to suspect that the culprit for this may be seasonal changes in my tap water so I will plan to mix my PO solutions in the future with distilled water.
Now, is there any literature which suggests that the clearing baths might also benefit from being mixed with distilled water.
Sandy