thank you for your interest, the tap water has been tested and is fine, all i can think is something has contaminated this tank (obviously) and I have taken every precaution. just going to empty and start again and be uber careful. weird as hell!Did you yourself test tap water? When I did my nitrate was 20ppm. So my tank always has 20ppm and up to 30 or 40. I keep an eye on it and do water changes as it gets high.