My wacky tap water


Junior Poster
Nov 22, 2008
After an extended absence (around 10 years) I have decided to start a new aquarium again, and want to do a planted tank. I live in a different part of the country from where I lived the last time I had a tank, and after looking at my municipal tap water reports and doing some testing I have found something quite unusual that I don't quite understand.

My tap water comes out with a PH of around 9.0-9.2, in spite of being quite soft, around 4.3 ppm of Ca and 0.8 ppm of Mg. If I then barrel the water and aerate or agitate the water for a few hours the PH will drop down to around 6.8, there is no detectable change in Ca, Mg, or alkalinity in the accuracy of my test kits. It looks like in the treatment process they are adding Alkalinity, Chlorine, Chloramine, Fluoride, Silica, and Sodium in addition to raising the PH by 2.5 points ( on page 9 for "Carroll Water" between the raw and treated water).

Why would the water have such a dramatic change of PH in such a short amount of time after coming out of the tap? This seems like it could be a problem for large or even moderate water changes unless I am willing to barrel the water perhaps overnight.



Lifetime Charter Member
Lifetime Member
Jan 24, 2005
Sacramento, CA
It looks like the water company is using a compound that raises the pH, but not the phosphate level. It also appears to raise the potassium level, but not by a lot in absolute terms. So, could they be using KOH, potassium hydroxide (lye) to raise the pH? In any case I don't see anything wrong with the water from the water report, other than the very high pH.

stevie D

Junior Poster
Oct 6, 2008
Cambridge water is very similar. It comes out of the tap quite high, 9+ and after sitting for a few days it will settle around 6.7. It has a low kh and repetitively low gh. I have a ph controller and i just add it right from the tap with some prime and never had a problem, even with discus.

Stevie D