Water too Acidic

[FishforJoy]

Hey guys! I am new to forum and trying to research why my very alkaline tap water turns very acidic in my 40 gal freshwater tank. It is not a new tank and this is a problem I have always had. I have removed driftwood. I have removed plastic plants and all rocks. The tap water is at least 8.4 which is common for our area. It is very hard. When I test the water in the tank after 48 hours it tests so acidic there is no color on my test strip. I have used crushed coral in my tank in the past to raise the alkanity and this has worked but folks around here still don't know why this happens. I usually don't worry about it because the fish I have have adjusted to the water, but when I try to add any new fish they just die (and quickly). So, I thought I would research some to see what you might have to suggest. Any help or suggestions are greatly appreciated.

 

[Coyne]

Have you tried a slower acclimation for new fish? I use a drip acclimation. The acclimation process takes a few hours, but its supposed to be the safest way to acclimate fish to new water.

Here's a link to the one I use:
Aquarium Acclimation Kit: Reef Gently AccliMate Pro

Im sure if youre crafty you could figure out how to just build your own for way less. Im not crafty though

 

[Cactuspixie]

Is your substrate inert?

It does seem very strange that the ph would swing so drastically in such a short time

If you can't identify the problem, perhaps you could switch to coral sand?