PH creeping up consitently

[mmcwhorter]

My pH is creeping up over a few days time. I'll take it down to 7.5-7.6 using MA/pool math and verify with the TF-100 test kit 6-8 hours later (all good), and a few days later it's looking like 8.0+.

Readings today were

FC = 3.5 at 0700
OCLT = 0 (measured last night at 1950)
CC= 0
TA = 90 (has been consistent for a long time)
PH = 7.5 (after about 30 oz MA last night)
CH= 300
CYA = 40
Borates= 23 (calculated from a virgin pool refill from municipal water x 7 76 oz boxes of Borax)

Water is crystal clear...can read a dime date at the bottom of the deep end. Really never been better.

Using 8.25% wAL mART bleach and Cal Hypo....alternating.

I am running a small PVC fountain that connects to the unused vac return line. It shoots about 10 fine streams of water up about 6 feet high and lands in center of pool at deep end. I always read that aeration will not cause pool PH to go from 7.0-7.2 only as high as 7.5 (this when you need to lower TA)......Since wife and kids like the fountain...I left it on thinking if it was t 7.5 it would stay there.

Should I disable it?

I do have an elevated spa overflow that is about 2 feet wide. The ledge spillway is 2" out over the pool...so there is some aeration there as opposed to it trickling down the spa wall in the pool. I have to circulate some water thru the spa to keep it from growing Algae, so stopping that it seems is not an option.

Thoughts? What other reasons would cause PH to go up in 2-3 days time and time again?

 

[Johnl]

It doesn't sound like you have a lot aeration, so my best guess would be the Cal Hypo. I am pretty sure that has a very high PH level.

 

[Texas Splash]

Aeration will certainly continue to raise your pH. I'm not aware of it stopping for any particular reason. Your fountain and spa if it is actively spilling-over will both contribute to increasing pH. You may also consider lowering your TA a bit more. Try for 80 first and see if that keeps the pH stable. If not, go to 70. Some will even use 60 if it means having a more stable pH based on their pool.

 

[mmcwhorter]

I was under the (mistaken?) impression perhaps that the Cal Hypo would tend to lower the PH "less" than bleach. Hence part of the reason I was alternating. Interesting observation.

I was also hoping the Borates would contribute to a more stable PH, as I am sure they do.

As to the comment on lowering TA, I hear ya...it was at 110 a few weeks ago. I took the PH down to 7.2 to lower TA using Pool Math and MA and the TA went to 90. PH came right back to 7.6 for a few days and kept going over and over to 8.0+ as I have been using MA more than I would like periodically to kick it down again to 7.5-7.6.

I'll kick TA down to 80 and see what happens....

I am assuming a good target PH is 7.6.

Thanks

 

[pabeader]

TA is one of the few things that I think just needs to be allowed to find it's happy place. My suggestion is to watch pH, lower with muriatic acid thus lowering TA at the same time. Eventually pH should settle down. The fountain thing is going to drive it up, so you might be fighting a loosing battle, but at some point the need to adjust should lengthen in time.

 

[JVTrain]

A proper pH target in a plaster pool depends also on your TA and CH levels. Use Pool Math and plug in all your current levels to see where your CSI is at. pH has the largest and most immediate effect on CSI. Using Pool Math, what pH range keeps your CSI at an acceptable range? Use that determined range to maintain your pH, only lowering it when the pH rises outside that range to minimize acid usage and avoiding having to add TA if it should drop below 60 ppm.

To note, adding bleach is a pH neutral process over the life of the FC added. That is, adding bleach temporarily raises your pH slightly due to the lye used to stabilize the bleach. When your FC returns to the level it was at before you added the bleach, the pH will be the same as it was before you added bleach. This excludes other sources of pH rise, such as aeration. I'm not sure if cal-hypo shares this behavior.

 

[JoyfulNoise]

Cal-hypo often contains small percentages of calcium hydroxide and calcium carbonate. Bleach has excess lye in it. Both of those will raise pH but it's usually not by that much.

Aeration will definitely raise the pH and the rise in pH is dominated by the over saturation of carbon dioxide gas in the water which is directly related to your TA. Even stagnant water outgasses CO2 (just at a much slower rate) and has a pH rise. So the advice to drop your TA is wise. Keep lowering it until you find the right value. Your borates are at 30ppm but TFP typically recommends 50ppm. In my own pool, I recently had my borates as low as 36ppm before raising them back up to 52ppm and I could definitely see a difference in the buffering when adding acid.