What I do: I use the pH, ammonia and nitrate liquid tests from API and test my water each month several days after each water change. I think I have done this for around 15 years. I follow the instructions exactly as described by the manufacturer who I applaud for trying to make an easy to use test which is accurate but fun to use! I've been keeping fish for many years, have six very varied aquaria some big some small, some planted some not. I am very pleased with the health and longevity of my fish which include 22 year old Clown Loaches and 10 year old Glass Catfish but I have always been worried about always detecting small amounts of ammonia. We are told we should have zero ammonia. My levels: My water company claims that pH is 7.4, nitrate is 10ppm and ammonia is officially 0.01ppm. Using the API kit my tap water measures pH 7.2, nitrate 5ppm and ammonia 0.25ppm. All my tanks achieve nitrate of between 5 and 20 ppm. pH measures 7.2 in all tanks. When using the ammonia test all my tanks always show some degree of greenish tinge in the predominantly yellow colour of the tube. I interpret the colour to be definitely above 0 but either at or below 0.25 in all my tanks. Some have more green tint than others but I do not think that the green exceeds the 0.25 in any of my tanks. Zero nitrate and ammonia: What has really interested me with this month's testing however is that I achieved a zero for both nitrate and ammonia for the first time ever. I tested my water butt outside from which I harvest daphnia. The water test produced a clear yellow on both the nitrate and the ammonia test meaning 0.00 for each. This is the first time I have ever seen a clear yellow colour for either test and I find it very interesting because it shows that the test kit can achieve a zero reading. Most importantly, it also finally convinces me that the ammonia level in all my tanks is always above zero. Interpretation: The manufacturer states that ammonia should be zero but I have not found this possible at any stage over the last 15 years. It would seem very reasonable to me to expect some ammonia to be present in aquaria all of the time. Fish excrete ammonia constantly and this has to be excreted into the water before it can make it's way to the filter and be processed. A water test will therefore detect it while it is in the water and on its way to the filter. The test also shows that in my case a variety of aquaria can show a small positive ammonia reading under 0.25ppm but also achieve success in keeping fish healthy for many years. Zero ammonia may be an unachievable aim in which case we should not be telling people they must achieve it. Perhaps the advice to fish keepers should be "Keep ammonia levels under 0.25 ppm if using the API test." I hope you found my post interesting! Understanding ammonia is at the core of our hobby so I really want to understand my findings.