Hi I currently have a newly set up 24 gal tank with two damselfish, one yellowtail and a black one. The black one just tonight started breathing really hard and is not eating. It seems to me that he might be in his last stages of life. He was doing fine before I replaced the filters in the back by putting in Chemipure and purigen from the stock filters. The yellowtail, however seems just fine. I tested the water and the Ammonia - 0, Nitrite - 0, Nitrate - 0, PH - 7.8. I know the PH is low but could that be the cause? I do have some diatom growth on the sand and am ordering a cleanup crew tomorrow. Is there anything I can do to save his life??