Running SWG Pool with High (8.2) pH

[joelq]

Hi all - our pool is going into its second full summer. It is ~11k gallons, IG with minipebble finish, and SWG. Since the very beginning, I've had to put put acid in (~32 oz every week) to maintain the pH and have just accepted this as standard for my pool.

Well, last weekend I had the idea of testing my pool water with the High Level pH Test Kit that I use for my saltwater reef tank. I've been testing it over the past few weeks and the pH has been staying steady at 8.2, with no additional acid, and with the SWG running at 30% (I run it at 40% during the heat of the summer).

So my question - can I just stop fighting the pH? Is it ok to just keep my pool pH at 8.2?

Thanks!

 

[JasonLion]

PH up around 8.2 can be fairly irritating to your eyes, reduces the effectiveness of chlorine, and it runs risks with possible scaling and metal stains. It is possible to balance your water so the PH will stop drifting up all the time without leaving the PH that high. Basically the higher the TA and the lower the PH the more PH will tend to go up. If you lower your TA the PH will stabilize at a lower PH than you have now. If you post a full set of test results we can make some specific suggestions.

 

[matj6876]

So, until Joel replies, I'll post to keep this thread going!

I'm in the same position - adding about 0.5 gal/week of acid. I don't really think I will ever be able to achieve the balance of which Jason speaks without changing my plumbing. (I cannot circulate my spa without running a fountain and a spillover - both of which raise pH, right?) So I have, for the last 6 months, run with a pH between 7.6 & 8.2, obviously sometimes it goes above 8.2, which is bad, but it would appear that I need less acid to run it between 7.6 - 8.2 than between 7.2 - 7.6

I have added borates this year and am willing to give it another go. So just now added enough acid to lower my pH to 7.2.

My numbers are:

FC: 6.5
CC: <0.5
pH: 7.6 (before the acid I just added)
TA: 80
CH: 480
CYA: 60
Na: 3600
Temp: 68F
Borates ~50

Questions:
How low can I safely take TA?
With the rest of these numbers staying the same, poolcalc says my CSI goes < -0.3 if I take the pH below 7.5 so really I've got to stay between 7.5 - 8.1 right?

Cheers

 

[joelq]

PH up around 8.2 can be fairly irritating to your eyes, reduces the effectiveness of chlorine, and it runs risks with possible scaling and metal stains. It is possible to balance your water so the PH will stop drifting up all the time without leaving the PH that high. Basically the higher the TA and the lower the PH the more PH will tend to go up. If you lower your TA the PH will stabilize at a lower PH than you have now. If you post a full set of test results we can make some specific suggestions.

Thanks, Jason. Here are my numbers:

FC: 4
CC: 0
TC: 4
pH: 7.6 (just added 40 oz of acid yesterday)
TA: 90
CH: 350
CYA: 60
Salt: 3100

I used to keep my borates level around 50, but stopped doing that when I read a thread (either on here or on PoolForum) that it can be bad for dog's livers. When I did keep my borates around 50, each time I add acid, my pH would drop, then climb quickly to 7.8 within a day or two. It would then stay at 7.8 for about a week before rising to 8 and beyond.

I have a weeping wall as well as a spa spillover. I've tried turning off the weeping wall, but didn't seem to do too much to slow the rise in pH. I think it's just my SWG that's causing the rise.

Thanks!

 

[JasonLion]

The key step is to bring the TA down. How low you can take TA depends on the CYA level and the borates level and is generally in the 30 to 60 range. joelq, I suggest you try TA at 60. matj6876, I suggest you try TA at 50. In this situation lowering TA is fairly easy, simply bring PH down to between 7.0 and 7.2, which will also lower TA, and the aeration already present will raise the PH back up. You may need to do this a couple of times to get to the desired TA. You may find that PH stabilizes at a reasonable level with TA a little higher than I am suggesting, if so you can stop there.

With significant aeration it generally isn't practical to try and keep PH as low as 7.5, but you should be able to stabilize PH between 7.6 and 7.9. Even if you can't get PH to completely stabilize, you will dramatically reduce the amount of acid you need to use by lowering TA and aiming for PH between 7.6 and 7.9.

One caveat, you will never get PH to fully stabilize when you have new, less than one year old, plaster/pebble.

Borates reduce the rate at which the PH rises, but they don't stop the increase. With borates you use the same amount of acid you used to use, you just add more acid less often. Another advantage of borates is that they help buffer the PH, much as TA does, which means that you can reduce TA a bit more when you have borates.

 

[Guest]

The biggest problem you will encounter in trying to run a salt pool with a high pH is that you are going to create scaling conditions (Not good for your cell or your pool suface) and it will interfere with chlorine production, which could mean you need to run the output at a higher percentage to maintain the FC which leads to a faster pH rise (cell output percentage is linked to how fast pH will rise!). Another thing to try besides lowering TA is raising the CYA to 80 ppm. This might allow you to turn out cell output down a bit and that should help also. If you have borates in the water you should find that your pH sits around 7.7 for a period of time (because of the borate buffer) then rises. The trick is to catch it when it hits 7.8 and not higher and then just lower it to 7.6. If you go lower ph will actually rise faster! These tips will not eliminate pH rise (it's the nature of the beast that a salt pool, particularly a plaster one, will need acid on a regular basis) but will help to minimize your acid use and keep your pool and cell from developing scale.
Remember that every pool is different and that some pools just need more acid than others, SWG or not! If you do have a large acid demand then perhaps a pH probe and controller for a peristaltic pump and acid tank might be a (somewhat costly) solution if the manual addition of acid every week or few days is too much trouble.

 

[duraleigh]

Check out Mas985's auto-acid controller. If it fits your situation, it requires no power and can be put together for little money.

 

[matj6876]

Jason - Thanks, I'll try it. I've never gone that low. Assume that TA value is "safe" long term? The reason I ask is if I shoot for a TA of 50 & pH of 7.6 (all other numbers being the same) I have a CSI of -0.5 in a plaster pool.

waterbear - Thanks for the tips. I have no probelms with the cell it's an IC 40 in a 15,000 gal pool. I run it at 4% for 6 hours a day and right now it keeps the FC at 6.5ppm, even in the full summer sunshine I rarely get close to 20%. 8)

duraleigh - I'm on that case too. I have an issue with water being drawn into the pump even when the system is off regardless of the height of the bucket relative to the pool & pump! I need more time to work on it before I post back there! :-D

 

[JasonLion]

At PH 7.7, TA 50, CH 480, CYA 60, Borate 50, Salt 3600, Temp 80 I get a CSI of -0.27. That is a little low but not dangerous. Plus it is unlikely that the PH would go down for long, so you wouldn't tend to go below maybe -0.38. If you increase your CYA level to 80 you should also increase TA to 60; actually you won't really have to do anything since the CYA will bring TA up by about that much.

 

[Guest]

Jason - Thanks, I'll try it. I've never gone that low. Assume that TA value is "safe" long term? The reason I ask is if I shoot for a TA of 50 & pH of 7.6 (all other numbers being the same) I have a CSI of -0.5 in a plaster pool.

waterbear - Thanks for the tips. I have no probelms with the cell it's an IC 40 in a 15,000 gal pool. I run it at 4% for 6 hours a day and right now it keeps the FC at 6.5ppm, even in the full summer sunshine I rarely get close to 20%. 8)

Bad news is that most of your aeration and pH rise is coming from your spa, not your cell since you have a short run time and a low output percentage. The only other thing that will help is to lower the TA even more. To compensate for the lower TA just raise the CH a bit. Actually, your CH is already fairly high. I am not a believer in the LSI, it can predict scaling (but pH is the MAIN indicator here) but does not accurately predict aggressive water in terms of plaster. I know that some people get hung up on it on this forum and others but if you came from PoolForum and you had read any of Ben's posts and info you know he did not put a lot into it either. Once again the MAIN thing that will cause damage to plaster is LOW PH and scaling is caused by HIGH PH. Both TA and CH must change by HUGE amounts to make small changes in the saturation index if you look at the actual mathamatical formula.