I dont know if you would get accurate results with dilution, you'd have to know the proper ratio, you could honestly email API if they have a dilution ratio for the kits. I know for red sea it only has instructions for nitrate dilution. Its 1ml of tank water and 4 ml of ro water.I have a question about my nitrite test. If the nitrites are so high that it's hard to read the color, can I dilute it with distilled water to get a "half reading" that's easier to discern? Or should I dilute it with new saltwater? The API Nitrite kit has the same color key for fresh and salt, so I imagine cutting the tank water with distilled would be okay.