I've volunteered my services as my parent's "pool guy" however I don't really have any previous experience so I've been going by some info I've gathered here and there. So far things are going OK, but I have one issue that I haven't been able to resolve.

First, some background. The pool was sitting for about 5 months before they bought the house so it was really nasty when we started with it. The plaster was trashed (discolored) so we opted for an epoxy coating to get us through a couple seasons and then intend to re-plaster then. We had a guy drain the pool, do the epoxy, refill the pool and install a salt water system for us. He flaked out and we can't get a hold of him so now we're on our own for the rest.

The salinity of the pool is 6500ppm, which I think is pretty high. When I started working with the chemistry 3 weeks ago the pH was 7.4 and TA was 200ppm. The local pool shop said to use muriatic acid to lower the TA and then bring the pH up with soda ash.

The acid lowered both TA and pH as expected, but the problem I ran into is the soda ash brought both back up together to the same place they were before.

Now after 4 gal of acid and 15lb of soda ash, I'm at 7.2 pH and 140 ppm TA. This seems to be the best happy medium I can achieve. 140 is not too far out of range and the pool is crystal clear so there are no symptoms of problems, but I'm concerned about the effects of having the TA too high.

Any suggestions for a way to get the TA closer to 100ppm and get the pH in the 7.4 range?

Am I splitting hairs here?

Dave,
Your sodium is 50% too high at 6500. You should be down around 4000 or less. The only way to address this is to pump out approximately half of the water in the pool, and then refill. There is no other reasonable way of removing the sodium concentrate. That will likely change your alkalinity as well.

If you were only dealing with alkalinity at this point, you would be looking to get it down into the 80-120 range. You would have to do that with acid, and then if you needed to bring the PH back up, you could use sodium bicarbonate (baking soda). Baking soda has less affect on PH than soda ash.

TA of 140 is definitely corrosive. If the pool weren't epoxy-coated, it would deteriorate the walls. But, it would also affect metals such as light ring etc.

One thing to keep in mind... don't make dramatic additions of chemicals. It's okay to put a little in and then check it a day later and see if you still need to adjust.

In the case of the sodium. You might be able to get away with draining 25% of the water and refilling, but I would go drastic on that one personally. I would do 50%.

Then, if you need to add salt back in, add less than what you think you need and check it a day later before adjusting further.
Al

Sounds good. I'll drain it at the end of the season. Thanks for the advice!

I just re-read this and wanted to clarify something...

Quote:

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Originally Posted by albinfla

If you were only dealing with alkalinity at this point, you would be looking to get it down into the 80-120 range. You would have to do that with acid, and then if you needed to bring the PH back up, you could use sodium bicarbonate (baking soda). Baking soda has less affect on PH than soda ash.

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Did you mean to say baking soda has less effect on alkalinity than soda ash?

No, my experience has been that baking soda has less effect on PH than soda ash. In other words, you can increase the alkalinity of the water with less affect on PH by using the baking soda instead of soda ash. If you're in a situation down the road and need to increase ph and alk, then soda ash will be a more effective treatment.

Quote:

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Originally Posted by albinfla

No, my experience has been that baking soda has less effect on PH than soda ash. In other words, you can increase the alkalinity of the water with less affect on PH by using the baking soda instead of soda ash. If you're in a situation down the road and need to increase ph and alk, then soda ash will be a more effective treatment.

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Ok, now I'm confused. My goal is to lower TA and keep the pH where it is (or later raise it without affecting TA).

If I lower the TA with acid, I've learned from experience that my pH will also tank. If I add baking soda to bring the pH back up, my understanding is that this likewise raise the TA back up. If this is true, I need another option.

Dave,
Yeah, I know it is confusing. I've been doing this for 20 years, and it still makes me scratch my head sometimes.

The issue with adjusting TA is that it is so closely related to PH, that they are not able to be adjusted completely independently.

Acid is the most effective way to reduce PH, but it also reduces TA almost proportionately.

Soda Ash increases PH, but it also increases TA nearly proportionately.

Sodium Bicarbonate increases PH, but does't affect TA as dramatically.

So, since there isn't a way to reduce TA only, you have to reduce PH and TA. Then, you use Sodium Bicarb to bring the PH back up without as much affect on TA.

Even the soda ash is not as proportional as acid... look at what you achieved above... you reduced both with acid and then you brought back the ph more than you brought back the alkalinity. If you did that same treatment again, you would probably be right back where you need to be on alkalinity.

The good thing is after you get it back right, it really is not that hard to keep it right. You make minor adjustments along the way. And, don't have knee-jerk reactions and over-react with too much chemical. Most unbalance in chemicals don't ruin your pool over-night, they take their toll over long periods. So, there's no reason to sweat it too much if it isn't just right.

You are still in a marginal range at 140. You could continue to monitor for a week or 2 and see which direction it tends to go. With the epoxy coating, it is not going to be absorbed into the walls. For that reason, an epoxy coated pool is much easier to maintain. You will probably be adding a gallon of acid per week anyway since the salt-chlorine generator will tend to raise the PH.

The best advice, check the chemical levels frequently, and make small adjustments frequently.
Al

Ok, I get it.

Does acid add anything (dissolved solids?) to the water that will eventually lead to a need to change the pool water prematurely?

You mentioned the epoxy and it's relationship to TA, so this may be a good time to mention this. The epoxy is pulling up from the plaster. We got a good rain after the guy put the epoxy on and there was about 18" of water standing in the deep end. The guy said this rain came before the epoxy was fully cured and caused the epoxy to peel. This explanation seems plausible since the epoxy is only peeling where the water was standing.

He said he was going to come back and re-do the epoxy at the end of the season, but he's since flaked out on us. I'm probably going to be doing the epoxy so I was wanting to know the best product to use, where to get it and if there's any tricks I need to know before taking this on.

Acid may add a small amount of TDS, I'm not sure. Your chlorine generator does add TDS though. It was probably over-salted after the re-coating. That would be the primary contributor to high TDS.

I do epoxy coatings frequently, mostly on industrial, or commercial concrete tanks. I also re-coated my own pool 3 years ago. It still looks great!

See this post for procedure. https://www.askmehelpdesk.com/constr...ighlight=epoxy

I have a local company that I purchase epoxy paint from. They call their paint "Plastic", which is appropriate. It gets very hard after full cure. They also have an excellent epoxy primer for concrete, it is a flexible sealer almost silicone like. They call it a membrane. If you can use the primer, you would need to get the surface very clean with most of your epoxy clean. Otherwise you could use the epoxy paint only.

The manufacturer tells me it doesn't reach full cure until 7 days. However, most of my projects have been done in 3 days... day 1 prep, day 2 primer and paint, day 3 refill. The product that I use is manufactured here in Tampa. It has been very good. You can go to my web-site and send me an e-mail. If you want me to ship you some, I could. They only sell to professionals. Generally speaking, it is cheaper than the stuff you buy online. And, I know it is good. I don't know about any other products except for Sherwin Williams, which is pricey.

More than likely, the guy who did it before didn't do the prep work properly. Or, the product he used was inferior.

The manufacturer of the stuff I use told me that if water goes back in too soon, that it will actually press the epoxy into the pores of the concrete and make it adhere better. But, he is not allowed to print that.
Al

Lower TA and PH together by using muriatic to between 6.8 - 7.0 PH
Aerate to raise PH without affecting TA.


http://www.troublefreepool.com/pool-school/lowering%20total%20alkalinity

If I were you I would have the epoxy completely removed from all of the surfaces. If the plaster underneath is in good shape(not being able to see the concrete, or peeling up anywhere(if it is peeling up you can patch it as well as the other areas if the gunite is shwoing through) and acid wash the pool and that will remove just about all the staining and discoloration in the pool. I had a pool that had gotten stained blue from some unknown chemical and I drained it and acid washed it and it turned out perfectly white. Just make sure if the pool is going to sit empty for any length of time to remove the hydrostat plugs