Low ph and high alkalinity?

xenayes99

Well-known member
May 30, 2017
91
Atkinson, NH
My pH keeps getting low, and I keep adding borax. Everywhere here is out of borax... alkalinity is high enough already though. Washing soda will also increase alkalinity, correct? Not sure what to do... what could replace borax and why does my pH keep dropping? Thanks

Ph 7.0
Alkalinity 80
FC 5
Cya 50
 

mgtfp

Bronze Supporter
Mar 5, 2020
288
Melbourne, Australia
If pH keeps falling then your naturally occurring aeration (i.e. not enforcing any more aeration than in normal use) is not (over-) compensating processes in your pool that reduce the pH. I am wondering if a slightly higher TA would increase CO2 outgassing to a level where it compensates your pH drop even without enforcing more aeration. But it's probably enough to just run jets for a while each week or run your pump a bit faster or buy some pool toys that will encourage more splashing to happen.

What is your CH? You certainly don't want to increase TA if you have high CH. And I think one of the processes that decrease pH, is calcium leaving your water and creating scaling somewhere. At 90°F water temperature and CH=1000, your CSI would certainly be in the scaling range at the upper end of the recommended pH range, and still slightly positive in the low 7s. In this case, the equilibrium of your water regarding scaling/corrosion (i.e. CSI=0) would be around pH=7. But I guess in NH you get enough rain that your CH shouldn't go up to these levels.

Usually your pool wants to tell you something by the equilibrium it's trending for. If pH trends are upwards, then that's usually easily explained by aeration. But I am not sure which processes there are, apart from the one I mentioned, that would result in an equilibrium with a low pH.

Not sure what the experts think about that.
 

xenayes99

Well-known member
May 30, 2017
91
Atkinson, NH
I haven't tested CH - I will do that. The pool temp is 90. It has been very hot and dry for the past 2 weeks - no rain. The kids splash plenty and I have the pool (filter and jets) running 12 hours a day now. How else would I increase aeration? I believe our pump only has 1 speed. I only use liquid shock (bleach). I did let the FC get to almost zero last week - I just lost track of time and the CYA had dropped to almost zero also, so that might have something to do with it? These have both been remedied and I'll keep on top of it better. The ph was low before that happened too though. We just filled our pool after getting a new liner last summer (tap water) so I don't have any old Crud from the previous owners in my water now. I will test CH and report back. I did find some borax on amazon and it is arriving Saturday. I guess I will just have to wait until then to address the ph.
 

mgtfp

Bronze Supporter
Mar 5, 2020
288
Melbourne, Australia
I just lost track of time and the CYA had dropped to almost zero
That might be a clue. Let's say you started at pH=7.7 and CYA=0. According to the parameters in the first post, your CYA was 50ppm. That means you must have added about 5kg of CYA to your 25k gallon pool. At TA=80, this would get your pH down to below 7. But because CYA dissolves very slowly, pH just keeps dropping until the CYA is fully dissolved. When did you add that CYA? Did you also add muriatic acid to adjust your pH before you added CYA?