NH3 high in my 2nd hand fish tank

[dongwy]

Dear all
I bought my 2nd hand fish tank (300 little) together with fish (15), coral, live rack, sands, and so on two months ago. I follow sellers recommentation and found out the NH3 always at high level, 2to 5 ppm. two weeks ago, I got biopronto and addin 10ml per day, and now the NH3 level keep around 2ppm and refuse come down, my fish , coral looks in good condition, and only feed them once per day.

any guru, know the reason why the reason why NH3 not come down.

[Xiggie]

Could be that the nitrate and phosphate are leaching out of the rocks ..overtime they will go away if you maintain good maintenance ..