Please help! We just got back from a week vacation. Brother in law was taking care of the tank for us and was shown and given detailed instructions. Today yellow Tang is almost dead and Koran angel died. Our tank was perfect before we left. Oh is 7.9, ammonia and nitrites 0, nitrate is about 80-90. This is AFTER 15 gallon water change and adding Prime earlier. Yes I use RODI water