It's a 30 gallon tank with sand and rocks that are over 3 years old. It's completely mature, nitrate, nitrite, and ammonia = 0, pH = 8.3. It's a good tank. I originally got a 12 gallon nano tank and got sand and rocks, then a 55 gallon which I tranferred the sand and rocks to, then earlier this year when I moved, I had to put the sand and rocks into this 30 gallon, so that's why I have such mature stuff but just now got fish...in case anyone was wondering or cares...if not, sorry for wasting your time...