Oddly enough, the less calcium there is the larger crystals will tend to form. With lots of calcium it will just go milky with lots of microscopic grains...Originally Posted by Michael Mutmansky
"Insoluble" is a relative term. Calcium oxalate is relatively insoluble, but still soluble enough that crystal growth will occur with low calcium concentration. Reducing the oxalate concentration enough to matter is not a viable proposition, you would have to go down to a few ppm to make any difference! It is much easier to eliminate the calcium.