Originally Posted by clayton1169
ph at the tap is around 7.1 the ph has never gone over 7.6 ammonia test crystal clear I can't find nitrate chart looks lite blue green in test tube ?? I also had a few pieces of driftwood in tank for plecos so I removed a very large piece cause a read driftwood can increase ph
Wood (real) will lower pH though very slightly, unless there is a lot of wood.
I suspect you are correct, the sand/gravel in the tank was probably coral or calcareous mineral. But a shift of only .5 should not cause fish deaths. As long as this is natural over the week and from water changes, and you are not using some chemical stuff to adjust the pH.
When you get new fish, you should acclimate them by floating the bag in the tank until the temp is equal. Then add some tank water to the bag (use a cup that is clean) and wait 15-20 minutes; then another cup and wait. Then net the fish from the bag into the tank, never add the bag water. Some use a pail for this, it is easier to manage. This prevents major shock from differing water parameters. I will assume the store is local and likely to have the same water as you.
As ammonia is zero that lets out it being some sort of mini-cycle with new fish.
I'll think about this some more, hopefully others may have some suggestions. I frankly do not think it is pH-related from what you've given us.