Hi again, thanks for your help, i really do appreciate. I done some water changes and its clearing up now. I do frequent water changes but my nitrates still won't low down. I own a reef tank. My tank is quite loaded with live rock, even in my refugium tank i have a big partition full of live rock. I don't have that great experience, you'll always learn, but i believe that it's not a bacterial bloom. My reef tank is been running for one year and nine months now and i think that bacteria is very strong now. What do you think?