It is chemically inert. It is commonly composed of quartz or other lime-free minerals, and will not affect water chemistry. A pH of 7.6 will not harm aquarium fish, as most of them are bred and raised in Florida fish farms and quite used to a high pH. If the fish are dying, you should check the ammonia and nitrite, not the pH. Also, check your alkalinity since the pH is low in the tap water. If your alkalinity is also low, this will cause fluctuating pH which can be an issue for fish. Last, but not least, monitor the fish closely as they could have a disease. If there aren't a lot of outward symptoms, but they don't seem to eat or are lethargic, they may have a protozoa or parasite.
Date published: 2018-05-11