I have at the moment a 10 gallon freshwater aquarium. (we have a 90 gallon also, but it has been shut down since we moved).
The little pH test kits always come with a glass tube, and somehow we always manage to break them. So I was guestimating how much pH down to add with each water addition. The fish seem healthy enough, though there are only 3 right now (black tetra, cory, and pleco)
We have a whole house filter that removes the chlorine and stuff, and then a water softener. We also have an RO unit for drinking water.
So I bought a new pH tester (bromothymol blue) (wish I had the TF100!!) and checked our tap water. Way above 7.6, the top of the scale.
Not thinking clearly, I also checked the drinking water. I was not remembering that ALL the water is filtered and softened, not just the drinking water.
Anyway, the pH of the RO water is pretty much neutral, maybe 7.2.
Why the difference?
(Please note I did not put this in the advanced section... need a basic answer!! Chemistry class was a LONG time ago!)