Arturs,get yourself a TDS meter,mix your RO water with tap water and aim for TDS of below 100 ppm. If you do not get a successful hatch at a TDS of 80 ppm,go lower and try by lowering the TDS to 60.I do not try to adjust the pH with my breeding pairs.The pH of my tap water is 8.2 and mixing 70% RO water the pH drops to 7.2.