Low PH in Well Water

[Dave1NC]

Hi there,
I am a long time member infrequent poster. I am a bit of a problem. I currently use well water as top off water. The well water PH is around 6.0. I also use vinegar and Kalk in my well water to keep my levels stable. Anyway I checked PH last night using Salifert PH kit and my PH was between 7.7 and 8.0.

I have good circulation - 2 Koralia Mag 8s (3250 GPH) and a Reflo Dart (3600 GPH) return. I also supplement Sodium Bicarbonate as needed to raise my dKH. My dKH is around 8.3. I have since added some additional Sodium Bicarbonate to increase to 9.3 hoping that will also raise the PH.

Does anyone have any other suggestions to keep my PH stable?

Thanks so much!

[Randy Holmes-Farley]

I don't think the well water pH has anything to do with the aquarium pH. Once you put lime into it, the pH is very high, regardless of where it started. Also, it may seem counterintuitive, but adding pure pH water at pH 6.5 to 7 does not lower the pH of seawater to which it is added to replace evaporation. It may even raise it. I discuss that below.

The aquarium pH is determined only by the aquarium alkalinity and the CO2 level.

Reverse Osmosis/Deionization Systems to Purify Tap Water for Reef Aquaria
http://reefkeeping.com/issues/2005-05/rhf/index.htm

From it:

http://reefkeeping.com/issues/2005-05/rhf/index.php#8

Final Effluent pH
Aside from the issues discussed above concerning the effluent’s pH when the DI resin becomes depleted, the final pH coming out of an RO/DI system should not significantly concern reef aquarists. Many aquarists with low pH problems have asked, for example, if their aquarium’s low pH may be caused by their replacing evaporated water with RO/DI water that they measure to have a pH below 7. In short, the answer is no, this is not a cause of low pH nor is it something to be generally concerned about, for the following reasons:
1. The pH of totally pure water is around 7 (with the exact value depending on temperature). As carbon dioxide from the atmosphere enters the water, the pH drops into the 6’s and even into the 5’s, depending on the amount of CO2. At saturation with the level of CO2 in normal (outside) air, the pH would be about 5.66. Indoor air often has even more CO2, and the pH can drop a bit lower, into the 5’s. Consequently, the pH of highly purified water coming from an RO/DI unit is expected to be in the pH 5-7 range.
2. The pH of highly purified water is not accurately measured by test kits, or by pH meters. There are several different reasons for this, including the fact that highly purified water has very little buffering capacity, so its pH is easily changed. Even the acidity or basicity of a pH test kit’s indicator dye is enough to alter pure water’s measured pH. As for pH meters, the probes themselves do not function well in the very low ionic strength of pure freshwater, and trace impurities on them can swing the pH around quite a bit.
3. The pH of the combination of two solutions does not necessarily reflect the average (not even a weighted average) of their two pH values. The final pH of a mixture may actually not even be between the pH’s of the two solutions when combined. Consequently, adding pH 7 pure water to pH 8.2 seawater may not even result in a pH below 8.2, but rather might be higher than 8.2 (for complex reasons relating to the acidity of bicarbonate in seawater vs. freshwater).