Actually, trisodium phosphate works. 2% solution gives pH of about 12. 7%, 12.4. 14%, 12.6. It's just impossible to adjust pH and buffering power independently over a wide range with a single agent like this. Apparently, Messrs is not interested in compensating effect so it makes little difference to him (except one is easier to mix than two).(posted 8094 days ago)One thing about pyrocatechin is that it has good chelating effect, and if the water is mineral rich this may deprive some of the developing agent. Trisodium phosphate also has chelating effect so it should help... especially if single stock solution is prepared just before use with some trisodium phosphate dissolved first into water. How much difference it makes? I don't know. I never had trouble with my tap water.