Yesterday I did a full water change (took the fish out, 99% of the water). I then used aqua safe aquarium water conditionor in order to use my tap water. After this I then used Easy Balance aquarium water condtionor. I have done this many times throughout the 3 years I have owned my fish and normally everything has been fine. I then fed them. My fish then starting coming to the surface for air. I tested the water and everything was fine apart from my PH levels were 6.0 when they are normally 7.0. I googled this and it said to change a third of the water as it may be due to overfeeding them. I changed a third of the water and all but 3 fish came down from the surface. One of these fish died that night. I then did a full water change to see if that changed anything. Another fish died. I dont understand why my fish had died unexpectidly. Please help!