coral is usaly not used in freshwater tanks, i raises your ph (unless that is what you want)
what kind of test do you use? dip strips, drops in a test tube?
how old is it? they go bad after a while and you will not give good reading. if you test kit is more then a year old you might want to buy a new one.
can you take a sample of water into you lfs
? most lfs
will do a water test for free!
what does you ammonia look like?
how much do you feed your fish?
what kind and how many fish do you have in the tank?