Constant PH drift

[el duderino]

My relatively new salt/gunite pool is experiencing MAJOR ph drift. I am putting in 2-4 cups of MA per day. I believe the major contributor is the massive amounts of aeration the pool gets from the 4 skuppers on the raised beam wall and the 26' negative edge. My analysis (per Leslie's which coincides with my own) is as follows:

FC: 2
CH: 250
CYA: 30
TA: 80
PH: 8.0 (but has been brought down to 7.4 since test)

My TA seems to hover in the 70-80 range, but the PH is a constant issue. I'm trying to stay on top of it rather than letting it get too high and then adding gallon plus to bring it back down. I typically add MA when the skuppers are on, as to circulate it more quickly. Also, the skuppers don't run through the filter/heater, so I figure there's less chance of damage going that route. Obviously, it adds to the aeration factor though, which I guess keeps my TA so low.

Please help me figure out what I can do to get my PH in check. Is this to be expected or a result of new plaster (Diamond Brite)?

Thanks!

 

[JohnT]

New plaster = rising pH.

 

[el duderino]

How long will this continue? I've had water since March.

 

[no-mas]

Second what John T said - can go on for 12-18 mos.

Obviously, it adds to the aeration factor though, which I guess keeps my TA so low.

Actually, aeration increases the pH. Adding acid and lowering the pH is what decreases the TA. Give it time, it will improve.

 

[el duderino]

Thanks for the replies.

Am I better off trying to stay on top of it daily vs. weekly when it requires masses of Muriatic and big swings? I would assume the answer is yes, but I have no basis for that other than the fact that I'm keeping the water closer to "perfect" at all times rather than just for a smaller portion of the week.

Would raising my CYA level help out here?

 

[JasonLion]

You have two things pushing up the PH, fairly new plaster and the negative edge. A negative edge pool causes large amounts of aeration, which push up the PH. Lowering your TA level to around 60 will help, but even then the PH will still be rising any time you run the negative edge. None of this has anything to do with the CYA level.

 

[frustratedpoolmom]

You can try using trichlor pucks, they will help keep the ph in check and will raise the CYA, which you can safely go up to 50 without any issues. If you have an inline chlorinator or floater. Don't put them in the skimmer unless the pump runs 24/7.

 

[polyvue]

Considering the size and newness of your pool, this doesn't seem like a major shift in pH. My 2 year old pool is 14K gallons and requires the same dose of muriatic acid (2-4 Cups) -- about twice a week. I think the pH increase is partly due to SWG operation.

Unrelated to the pH issue: Increasing CYA from it's present value of 30 (to 40-80) is probably a good idea. You'll have to increase the SWG's chlorine work by dialing up the percent a bit or extend pump operation time (to conform to FC > 5% of CYA.)

Finally, I would hesitate to add pucks to a SWG pool.

EDIT 9/4/2009 - Though it would seem logical to increase SWG output in order to increase chlorine production after adding cyanauric acid (CYA), in practice the opposite may be indicated. Upon increasing the CYA level in my own pool recently, I had to decrease SWG output to maintain the same levels of Free Chlorine (FC). Go figure. END OF EDIT 9/4/09 polyvue

 

[frustratedpoolmom]

In the first year of a plaster pool it's not uncommon to use trichlor pucks via inline chlorinator to control the PH rise, build the CYA level to where it needs to be, then switch the chlorine source to the SWG.

 

[PaulR]

Am I better off trying to stay on top of it daily vs. weekly when it requires masses of Muriatic and big swings?

I would be inclined to wait for it to reach 7.8, however long that takes, then bring it down to 7.2. Keeping it within those bounds shouldn't damage anything.

Bringing up CYA is independent of all this; Pool School's Water Balance for SWGs suggests 70-80. Using trichlor will help some, I would still expect you to need MA periodically.
--paulr

 

[polyvue]

In the first year of a plaster pool it's not uncommon to use trichlor pucks via inline chlorinator to control the PH rise, build the CYA level to where it needs to be, then switch the chlorine source to the SWG.

I guess that accomplishes the same thing as what I did on start up: check pH frequently, adding MA in small amounts and tweaking the SWG as needed. I add CYA directly. When CC > .2 I shock the pool with powdered trichlor (not pucks) which adds a bit to CYA, but not enough to accrete to an excessive level. Due (presumably) to splash-out, I have to add CYA every couple of months.