hi guys so I know quite a bit of knowledge about the nitrogen cycle and just got my second tank being a 10 gallon... anyways went to a friends house and we found her kids old fish tank! It was disgusting because there was a dead fish in it and she said it has probably been dead in there for over a year! Filter was still going and besides the fish the tank was spotless!! So I took my testing kit over and checked all the levels Everything as so perfect! pH, ammonia, nitrites, nitrates I took some gravel and started up my new 10 gallon tank with no fish in and added the gravel!! I am now regretting it thinking the dead fish could have created other problems such as parasites! What do I do?