PH constantly rising....

[tcat]

I need to add 24 oz. of MA every 2 or 3 days to keep my pH at 7.5-7.6.

FC = 4-6 (during any day or week)
CC =0
PH = 7.6 (seldom, but is yesterday)
TA = 70
CYA = 35
CH = 300
Borates = 45-50

15K gallons, 50% shade. What can adjust to try to keep pH from moving? Add a Puck once a week?

 

[chem geek]

Re: How to keep PH from constantly rising....

So it appears you don't have a saltwater chlorine generator (SWG/SWCG) and your TA seems reasonably low and you aren't trying to lower the pH below 7.5 (I presume) so do you have significant sources of aeration such as a waterfall, spillover, fountain, etc.? Was the pool re-plastered recently? Are you using a less expensive bleach as your source of chlorine that perhaps is high in lye (sodium hydroxide) content?

Your FC is higher than usually needed for your CYA level -- is there a particular reason for that? You could use Trichlor pucks to supplement chlorine and that will be like adding some acid so should help with the pH and it will raise the CYA level. You could target 50 ppm CYA and then stop with the pucks. You may then find a lower daily chlorine loss (if you keep the FC in the same 4-6 range with 4 an absolute minimum) so by adding less chlorine that might help with the pH.

 

[tcat]

Re: How to keep PH from constantly rising....

None of the above, no aeration etc... Clorox 8.25% from Sam's... 4 year old pebble non-salt pool. My CYA use to be 50 and I have my auto Chlorine feeder set to make sure FC hits 5 or 6; seems to have drifted down to 35-40 over the past couple months (rain/drain/backwash). With about 2 ppm drop it'll hit 4.0 before pump starts sucking Clorox. Still a little high, but with an auto feeder I want to be safe (since I can forget to check it for a few days). I've had to add pH at about the same rate since day 1 (with CYA at 70, or 35). Just curious as to what is "normal" PH rise (if there is such a thing as normal).

 

[chem geek]

Re: How to keep PH from constantly rising....

Without aeration and with a reasonably low TA, your acid usage is more than usual so that's a bit of a mystery. Clorox usually has the lowest amount of lye of all bleach brands (pH of the bleach is around 11.9, though that was with 6% so I'm not sure if that's still the case for 8.25%). If the pH rise is from carbon dioxide outgassing, then you should see the rate slow down if you let the pH rise. See if the rate slows down as it gets to 7.8 or 8.0. If not, then there is some form of base getting added to the pool, but usually that's either from the lye in chlorine or from plaster curing.

At 6 cups of full-strength Muriatic Acid (31.45% Hydrochloric Acid) per week (I assuming you are using full-strength and not half-strength 15-16%) in 15,000 gallons, that would lower the TA by 12.5 ppm if the pH rise was only from carbon dioxide outgassing and your pH would get lowered from 8.0 to 7.6 or from 7.8 to 7.35 (assuming 50 ppm borates you listed). Do you see your TA dropping over time? If not, then either that means the pH rise is from a base or that the TA is increasing from evaporation/refill though it would take a lot and/or be very high TA fill water.

 

[ahampleman]

Re: How to keep PH from constantly rising....

Clorox usually has the lowest amount of lye of all bleach brands

With that be stated, what is the lye content of 10% bulk Chlorine you fill up the jugs with from the Pool store? Would I be better off spending more for the Clorox at Sam's? Reason I ask, is I have the same PH / TA issue with a 8 year old plaster job. :? 100% BBB'er and loving it!

 

[tcat]

Re: How to keep PH from constantly rising....

I do see TA dropping. 90-80-70.. maybe 65-70 now (4-6 month period). I need to check my fill water, but I assume is fairly neutral. I don't think pH has gone above 8, tends to "settle" at 7.8. The TF-100 kit color chart seems "faded" compared to the actual test liquid, I have a hard time deciding 7.8 +/-2 (I actually tend to think test strips work better for this test... but I don't...). I think I'll raise my CYA back to 50 to see what happens.

 

[chem geek]

Re: How to keep PH from constantly rising....

High quality chlorinating liquid has a pH of 12.5 so per FC is still somewhat higher in lye content than Clorox bleach, at least the 6% stuff. Poor quality chlorinating liquid has a pH of 13 or higher and would noticeably raise the pH of the pool. I doubt that the problem is the bleach -- even with having "too much" lye, it wouldn't cause as much rise as is seen and you'd have everyone seeing this if they used a similar brand.

With the TA dropping, that implies that the problem is indeed carbon dioxide outgassing since your acid additions are lowering the TA rather than just counteracting a base. With your now lower TA, why don't you just not fight having the pH lower than 7.8. The only issue with higher pH is the risk of metal staining, but if you don't have metals in the water then that's not a problem. Since your TA is low, having a higher pH is not a problem for calcium carbonate scaling unless your CH was quite high. Could you have an air leak on the suction side of the pump causing aeration?

 

[fast1971chevelle]

Re: How to keep PH from constantly rising....

if you have a Rural King near you they have the 31.45% M/A for 2.99 a gallon and the 10% liquid shock for 9.99 a case 4-1 gallon jugs......Mike

 

[sb127]

Re: How to keep PH from constantly rising....

I finally gave up on chasing PH. Mine seems to always settle at 7.8 when using bleach as the sole chlorinating method. If I use pucks while on vacation, the PH drops to about 7.5. If everything else in in check, CSI is near zero and I haven't had any negative effect in a couple of years.

 

[tcat]

Re: How to keep PH from constantly rising....

Would cost me about $400 in travel to the closest Rural King... making the cost per ounce a tad high.

I put 4 pucks in my auto fill for this week. Will leave things as is after that and live with 7.8. I've seen no ill effects over the past year. Thanks for all the info and suggestions!

if you have a Rural King near you they have the 31.45% M/A for 2.99 a gallon and the 10% liquid shock for 9.99 a case 4-1 gallon jugs......Mike

 

[mikeybats]

Re: How to keep PH from constantly rising....

I've been battling the PH rising by adding muriatic acid for years. I attributed the constant rise to waterfall aeration. Calcium is at 230 and borates are somewhere between 30-50 based on the test strips.
What I get from this is that I shouldn't focus so much on the TA which is usually 60 but instead add calcium to get closer to 450 and then see if my PH stabilizes ?

 

[chem geek]

Re: How to keep PH from constantly rising....

Welcome to TFP!

No, you shouldn't take that away from this thread. CH is not normally relevant towards rising pH. You can certainly increase your CH if you want to if it helps make the saturation index be more balanced, but I don't think it will change your rate of pH rise. Try turning off your waterfall and see if the rate of pH rise and amount of required acid added changes. If it does, then you correctly identified the primary source of pH rise.