I am posting this for my brother he got a 75 gallon tank about 6 months ago. He set it up and cycled then transferred fish from his 29 gallon they didn't last a week. he checked the ph, ammonia, and nitrate all were fine. he asked his lfs they told him to empty the tank and scrub it down with 1 part bleach and 4 partswater he did that and set his tank back up. got the levels were they needed to be, cycled. then once again he put fish in and the died finally right before christmas he got some to stay alive. they lasted about 2 weeks and died. What can be causing this? All his levels are fine, temp is good. he has been doing frequent water changes and just can't keep the fish alive. He has a big black ghost that has outgrown his 29 and he wants to move him to his 75 but doesn't want to kill it. What should we do?