How to calibrate my ph meter?
I just bought a digital ph meter. It came with
6.86 powder and
I mixed two solutions. One with 1/4 cup of tap water and 6.86 solution and one with 1/4 cup 4.00 solution.
When I place my meter in the 6.86 ph water, I calibrated it so it's around 6.85
But when I place it into the 4.00 ph solution, it reads 4.3. I'm stuck on how to calibrate it.
I tested it In my fish tank with 7 ph tap water buffered by Amazonia new and it reads less than 6 ph. Something's wrong. I know the ph should be around 6.5 that's what my liquid ph tester reads. So the meter is calibrated low. But eve if I crank it up, the 4.0 solution and 6.86 will be too high. What do I do?