SWG pool -- getting and keeping the pH down

[PhillipH]

I just got my pool last August (3 yrs old at that point), and it's a SWG pool. From day 1, the pH has been high and has been very stubborn to get into range. It was around 8.2 to start with. I used dry acid in my attempt to lower it. I slowly and steadily added alot of sodium bisulfate over a 3-week span (2 bottles -- 12 lbs), but it didn't have the affect I expected. The lowest I ever read was 7.8, but the majority of the time it would be 7.9-8.0. I struggle to have confidence in my reading of the color scale, but these are my best guesses. The sample remained some shade of purple, so I know it wasn't in the 7.4-7.6 range. I then gave up and shut down for the winter.

Fast forward to this spring. I've began using muriatic acid to try to lower it. See below for the gross details. I've added what seems like quite a bit of acid, but the pH is still very slow to move. Am I missing something, or should I just keep doing what I'm doing? I know that SWG pools tend to constantly push the pH up, and I know that I'll probably require a regular "maintenance dose" of muriatic acid to maintain pH in range. I'm just surprised that it's so hard to get it in range.

Can you guys give me a feeling of what life is like with a plaster/gunite pool with SWG, and if this is typical?

I love my new test kit btw.

[attachment=0:3j3dth1s]pool.jpg[/attachment:3j3dth1s]

 

[257WbyMag]

SWCG pools do tend to have pH upswings that need more frequent attention than other pools do and this is just their chemical nature. It's good that you have been using muriatic acid to make your adjustments as it is easier to dose and doesn't add extras like the pH down granulars do.

Have you considered lowering your TA? By getting your TA down to 70 or even 60, you might be able to tamponade the pH rise a little better.

BTW, a pH of 7.7 is still fine. Some pools just like to live at 7.7 and not the perfect 7.4 that we all wish for.

 

[JasonLion]

Your experience is fairly typical for a SWG owner that hasn't visited Trouble Free Pool before. If you follow our recommendations things will be very different. I have a SWG pool and din't need to add any acid all of last season, aside from an initial adjustment on opening.

There are two obvious problems here. Your CYA level is way too low for use with a SWG and your TA is a little too high. With a SWG you should maintain CYA around 70 to 80. That will help in a number of ways, both increasing the life of the SWG cell and reducing the amount of PH drift. You are also maintaining TA too high. You need to let the TA go down to the 60 to 70 range, or perhaps a little lower. Adding borates can also help slow down PH drift, though it isn't really necessary.

There is a good review of what the ideal levels for use with a SWG are in the Water Balance for SWGs article in Pool School.

It is better to use muriatic acid rather than dry acid. It is less expensive and better for the pool. It is a little more dangerous to handle, but as long as you stay away from the fumes it isn't that bad.

 

[PhillipH]

Keep in mind that I'm not new to TFP. I've read alot of posts over the past 6-8 months since I got my pool. TFP is my #1 resource for info and for learning. So, what am I not doing right regarding TFP recommendations? You detailed the CYA and TA, and I'll address those below. Anything else? I don't think I'm very far off. My biggest question is why it's taking so much mur acid to lower my pH.

My TA was in the 100-120 range last fall, and it has been slowly coming down. I guess this is due to me adding dry acid and mur acid, b/c I really haven't added anything else besides Ca (and salt). My latest TA with the TF-100 kit was 80, so I'm getting there.

Regarding my CYA, keep in mind that I'm still getting everything in range. My CYA was much closer to 80 last fall. I drained some water last fall and we got alot of rain over the winter, so I guess that lowered it. I do need to add some CYA and will do so very soon. I just haven't considered this critical since we aren't into summer yet. I've had my cell dialed back to 20% and the pump running 8am to 5pm, and my Cl is still 8.0.

Thanks.

 

[frustratedpoolmom]

When you calculate for lowering the PH with Muratic acid, what is your target?

If you are targeting 7.4-7.5, you might have more success with a target of 7.2.

By repeating these acid additions, your TA should drop down a little bit more - I think by the time you get to 70 you should see your PH drift stabilize, especially if you increase your CYA back in to range - this should allow you to reduce the %/run time which should also reduce the tendency of the PH to drift up.

 

[PhillipH]

I've done the calc a few times, but I can't remember the exact target. Probably 7.5. Recently, I just decided that I'd repeatedly add 1 Pint every few days until the pH got to where I wanted it. Reason being, going by the label directions (dry acid) or the calculator results doesn't even budge the pH. It's not nearly enough.

Does my high chlorine level have any upward bias on the pH? I've read too much and can't remember.

I'm already pretty low on my SWG % and my pump run time, but I definitely plan to get the CYA up this week.

Thanks,
Phillip

 

[JasonLion]

The more the SWG runs, the more upward pressure there is on the PH. Low CYA and high FC levels both make the SWG run more.

Something strange is going on with you TA levels in the chart if you haven't been adding baking soda or soda ash. You have had TA go from 70 to 90 at least twice, which it shouldn't be doing on it's own. Maybe that is just testing error from before you got the TF-100.

You probably want you CH level higher.

 

[flintstone]

You may want to change some of your chemical additions in an effort to move closer to the ideal ranges and to see just how they effect your pool, since every pool reacts a bit differently.

The closer you get to a CYA level of 80, the less you will have to chase rising pH. It makes a huge difference. Don't stop at 60 or 70 thinking that's close enough. You may have to buy more cyanuric acid reagent to do all the testing, but do it. Add a pound at a time over a few weeks until you get to 80. You can't rush this chemical addition anyway, as it takes a week or so to show up in your tests.

Stay away from dry acid. Try adding 2 pints of liquid muriatic acid when you dose. Test an hour or three later. See what it does to your pool. I add two pints at a time and use about that in a week during the spring, less in the winter and more in the summer.

Shoot for an FC level closer to 3.0. I know this site suggests a bit higher, so shoot for 3.5 or 4.0. I'll bet your manufacturer suggests a lower level than 9, though. Dial down your swg "on" time or pump run time for now. As bather load increases and as temperatures increase, you will need to dial it back up. See what it does to your pool.

Over the winter, I turned my swg off and had almost no pH rise.

Perhaps I do need to run a disclaimer. My pool tends toward scaling, and I am no expert. The pool calculator still confuses me (Just how much liquid chlorine do I need to shock?). But it will be interesting to see how changing a few parameters will affect the water chemistry of your pool.

 

[PhillipH]

Thanks for all the help. Probably just testing error. The difference b/w 70/80 or 80/90 is just one drop, so that's not much resolution. Also, the recent change from 70 to 90 was with 2 different test kits. I'm now using the TF-100. I've never added baking soda or soda ash.

flintstone, you are saying that 2P per week is a typical maintenance dose for your pool throughout the year? And more during the summer? I'm very interested to hear from people regarding typical weekly maintenance doses. 2P per week every week seems like alot, but given what I've seen with my pool, I can believe that much is necessary to maintain pH.

CYA target is 80. From PS recs, MinFC % is 4.5% for SWG and target is 7.5%. So, my MinFC would be about 4.0ppm and my target would be about 6.0ppm. Correct? I also see some discussion of "3-5ppm FC" at the PS, so I would benefit from some clarification.

Is liquid, solid, or granular CYA preferable? The solid takes a long time to fully dissolve, so why not go with the liquid or granular?

I do plan to increase the CH next week.

 

[JasonLion]

For the pros and cons of the various forms of chlorine, see this article in Pool School. For most people here the best choice is bleach/liquid chlorine.

Yes, with CYA at 80 and a SWG you want to keep FC between 4 and 6. That is the range that we have found to be trouble free. Other sources tend to recommend lower levels and then assume that you are shocking the pool weekly to take care of the problems that you will eventually have at lower levels.

If your plaster is less than one year old, then 2 pints of acid a week is probably a little low. Otherwise 2 pints of acid a week is a lot more than I would expect you to be using once the TA comes down some more.

 

[PhillipH]

I was asking about CYA, not chlorine. Thoughts about the various forms that CYA comes in? My pool is SWG, and I don't use any extra chlorine.

My pool is almost 4 yrs old. Please see my other thread regarding why we want TA so low wrt my concerns about a very low CSI.

Thanks,
Phillip

 

[JasonLion]

Sorry!

The best source of CYA is granular stabilizer/conditioner. It has different names depending on where you shop. It is the least expensive by far and the whole "slow to dissolve" thing really isn't a problem.