PH keeps rising

[Devon]

Alkalinity is 80, calcium hardness 220, TDS 1000, Phosphates 0, CYA 40. Chlorine stable at 2+ppm. I use 3" trichlor tabs but still am constantly adding acid, I can take the PH to 7.4 and a day later it is 7.8 or 8.0 - I have 3 pool supply houses here (Leslies and 2 small independents) and none of them have a clue why. About two months ago, due to high Calcium, high TDS and high CYA. I drained between 1/3 and 1/2 of the pool. My tiles were badly scaled so before draining, I added 2 quarts of BIO-DEX Protectall Supreme, filled the pool completely and ran the filter for 3 days straight (at their suggestion). This was supposed to soften/loosen the scale which it completely failed to do. I hand scraped the scale with more razor blades than I care to remember, then ran the pump for another 2 days to vacuum up any scale I could. I then drained and refilled the pool, re-balanced the water as per the "experts" advice and all was fine for over a month. This PH thing is 3 weeks old now and I have done nothing but add acid and tabs.

Any ideas would be greatly appreciated.

I'm not sure if my filling in of pool stats took, so here goes
39x19 feet shallow 3 deep 9
white plaster
25-30,000 gallons
hayward 60 sq ft DE filter
1 HP Whisper-Flow Pump
10 hrs/day
Kreepy with dedicated suction port
very very low swimmer load, very few leaves, etc

[aylad]

You might find that your pH is more stable if you would raise your TA a bit to the 100-120 range. The lower TA is recommended for non-stabilized chlorine sources, but with the stabilized ones, the higher TA seems to keep pH more stable. I can't explain chemically why this is, but if you want a full explanation, I can get Waterbear, Chem-Geek, Pooldoc, or some of the other chemistry-types to explain it. Anyway--I don't know anything about the BIO-DEX product you used, but it's possible that either it or the dissolved scale is part of the problem too.

Also, any form of aeration will make the pH rise--do you have waterfalls, fountains, spillovers, etc? Are your return eyeballs pointed upward so they rifle the surface of the water?

[waterbear]

Higher TA will help keep pH from dropping when using stabilized chlorine but if pH is still rising then you have to find the source. Higher TA actually causes pH to tend to rise because of increased outgassing of CO2. Outgassing of CO2 is a main cause of pH rise in pool and aeration (from fountains, negative edges, water features, etc) increase aeration and therefore pH rise. Also, the lower the pH the faster it rises. TA is basically a measure of the amount of bicarbonate in the pool water which is in equilibrium with carbonic acid and this is our buffer. Carbonic acid is basically CO2 dissoved in water (think seltzer). The higher the TA the higher the bicarbonate and therefore the higher the carbonic acid (to keep the equilibrium). The lower the pH the more bicarbonate is converted to carbonic acid (carbon dioxide in the water). The more the aeration the faster the CO2 gasses off (think shaking the bottle of seltzer to make it go flat). The BIODEX products are mystery products, no one knows what is in them and if I don't know what something is I do not put it in my pool.
Bottom line is this. IF your pH is rising and you don't know why lowering the TA often helps. Not dropping the pH below about 7.6 often helps. Adding borate to 50 ppm definitely helps.

[Devon]

3 pf the 4 return eyeballs are pointed slightly up, water does ripple, 4th one is a diverter eyeball pointed 45 degrees down, that was done to help the Kreepy Krauly get to the shallow end. No waterfalls , fountains etc. I did get the TA up to 100 a while back by adding a LOT of baking soda, after slowly adding acid the next day over a period of a few days, the Ph settled at 7.6 but TA was back down to 80.

The Protectall Supreme MSDS just says "Non-Toxic Cleaning Compounds & Bio-Degradable Surfactant". In hindsight, I agree with you, waterbear, a lesson learned here. Never heard of adding borates, will do some reading. My elementary chemistry knowledge tells me that whenever 2 molecules of HCl meet one molecule of NaHCO3, they react and create salt and carbonic acid (NaHCO3 + HCl → NaCl + H2CO3). Could easily be wrong, maybe someone can agree/disagree with this.

Thanks and I'll post back in a few days with updates on the water chemistry.

[CarlD]

Do you use a solar cover? If not, I'd consider getting one as it will interfere with the out-gassing from aeration that raises pH. Also, point your returns further down so there's little bubbling. BTW, is your pool new? If so, you may well be dealing with curing, which is typical of new hard-sided pools..and the curing raises pH, too.

You gave us current CH and TA numbers, but what were they before you drained the pool down, when you got the scaling? You shouldn't have scaling with your current #s.

I find I frequently can run TA far lower with stable pH--like as low as 60ppm, especially if I've seen pH rise.

Just some ideas...

[Devon]

No Solar Cover, returns do not cause any bubbling, just some ripples. I will point them further down. Pool was re-plastered in 1995. Before draining CH was 390, TA was 120, CYA was 120, pH 8.0.

Over the last week here is what I have done and the results:
TA was at 70 so I added 2 lbs of Bicarbonate every day until it reached 90. I add it when the pump first starts up and I add it by mixing it with 5 Gal Water, stirring extensively than using a home-made siphon to spread the solution all over the pool surface. When the 5 Gal bucket gets low I add more water and stir again then spray again, this is repeated 3 or 4 times until there is no more Bicarb that has not dissolved. After 4 days TA was 90-100 pH was 7.8-8.0. I then added 8 oz HCl a day and after 3 days the pH was 7.6 but TA was back to 70. I am being told by the local stores that at some point this should stabilize and not need Acid or Baking Soda added every day....

[Watermom]

I think you are making your bicarbonate additions more difficult than is necessary. Just dump the stuff slowly into the skimmer in small increments or in front of a return jet when the pump is running. No need to predissolve it and using a siphon to add it.