Originally Posted by tomncassie
I have seven koi angelfish,five lemon tetras,ten penguin tetras.Ammonia .25 ,nitrite 0,ph 7.4,nitrate 5.0.I believe that I have very hard water.I plan on getting a test kit for the hardness.I have slowly lost some fish one by one moslty after a my monthly gravel cleaning and close to a 50% water change.I also do about 1/3 water changes a week.
On the fish loss, do you mean one dies after every water change when the gravel (substrate) is dug into? This suggest something is amiss down there. And the ammonia above zero might be connected.
Are there live plants in this tank?
On the hardness, before spending money on a kit you may never use again, check with your water supply people, they may have a website with data posted, or be able to tell you. A pH of 7.4 does not suggest overly hard water, but that can vary. I would not expect the GH to be causing the deaths, given the timing issue, though too hard water can damage fish organs and weaken them, so other issues have more impact.