Not a bad idea to go and try another test kit.
For the fish to be thriving like you describe then obviously your water is ok, but to have a reading of 8ppm on one tank and 0 for tap water and 0 for your other tank, something isn't right. I have an 8pi test kits from 5 years ago, and they read exactly the same as the api master test kit I purchased 3 months ago.
For the fish to be thriving like you describe then obviously your water is ok, but to have a reading of 8ppm on one tank and 0 for tap water and 0 for your other tank, something isn't right. I have an 8pi test kits from 5 years ago, and they read exactly the same as the api master test kit I purchased 3 months ago.