Muriatic acid SEEMS to have little effect

[jamescox]

Customer has a 15000 gal pool that's been down for a while. It's not green, but is cloudy. They're trying to clear it up, but before they can SLAM, we're trying to get the pH down. The muriatic acid seems to have little effect, and I'm suspecting an air leak. Tests are as follows:

Date	ph	TA ppm (CYA corrected)	CYA ppm	Temp Deg F	Waterlink Software Acid needed (31.45%)	Pool Calculator (TFP) Acid Needed (31.45%)
9/7/22	8.7	121 (120)	5	83	48 oz	59 oz
9/14/22	8.5	116 (113)	5	81	48 oz	53 oz
9/16/22	8.2	135 (134) bad result?	5	80	36 oz	58 oz
9/22/22	8.4	114 (113)	5	82	48 oz	51 oz

Notice the customer is bringing a sample several days apart. Customer is a Remax agent, so cannot seem to dedicate enough time to this pool, but I'm still confounded. They are trying to run the pump 24 hr/day but they say "leaves keep getting into the drain". I have obviously recommend they remove the debris before continuing and also trying to get where they can test more often.

In the mean time, out of pure curiosity, I'd like to know to know what could be raising the pH so quickly. Not a SWG, they use Sodium Hypochlorite, hasn't rained often. It would be nice to have tests shortly after the acid is put into the pool. I'm curious to know if the drain being clogged could be revealing an air leak. Customer also mentioned they have had to add water, but didn't say how far apart.

 

[Texas Splash]

James, an air leak wouldn't be the cause. The pH is rising from factors such as:
- An elevated TA level. The TA numbers above are not from a TF-100 or Taylor K-2006C, so that's a concern. But if they are accurate, there's lots of room to lower the TA.
- New fill water generally increases the TA and pH.
- Aeration. If there are any water features in use that would do it as well.
- New plaster - if it applies.
- Using low strength (14%) muriatic acid versus the full strength when dosing.

Accurate testing and being there on a regular basis are certainly two big factors that could impacting the results of lowering the pH.

I would also make mention that the CYA number listed above (again, if accurate) is much too low. Refer to the FC/CYA Levels for more info.

 

[jamescox]

James, an air leak wouldn't be the cause. The pH is rising from factors such as:
- An elevated TA level. The TA numbers above are not from a TF-100 or Taylor K-2006C, so that's a concern. But if they are accurate, there's lots of room to lower the TA.
- New fill water generally increases the TA and pH.
- Aeration. If there are any water features in use that would do it as well.
- New plaster - if it applies.
- Using low strength (14%) muriatic acid versus the full strength when dosing.

Accurate testing and being there on a regular basis are certainly two big factors that could impacting the results of lowering the pH.

I would also make mention that the CYA number listed above (again, if accurate) is much too low. Refer to the FC/CYA Levels for more info.

Thanks so much for the response. My Waterlink Spinlab has done me well so far, all of it's recommendations have generally gotten the pH to 7.2 very precisely, except for a short time it went out of calibration, so I trust it. I've also got a Taylor test kit that I periodically compare for accuracy.

On the points you listed,
- I have set his TA target to 50, not because it's SWG, but because it rains daily here for much of the year. I'm unsure how to go about destroying alkalinity without aerating the pool and adding acid. So my plan was to continue to address the rising pH until TA falls to normal range.
- New fill water might be a possibility, I'll ask him how often he's putting water in
- Aeration is what my thought was on the air leak suction side, thinking the air being sucked in would aerate, but to be honest, I'm not sure how that would off-gas CO2. There are no water features that I know of
- Vinyl liner throughout, so no plaster
- low strength muriatic acid: Can you expand on this? or recommend some reading so I can understand this better? I have been to Acid - Further Reading, but I didn't realize the strength mattered when dosing, so long as you adjust the formula. I have just been able to get the Transchem 31.45% half the price of the 15%. Just want to make sure I'm doing right by my customers.

CYA product is there, customer just needs to get it in their pool. I suggested he get it up to 30 ppm

I think your point about adding water is the key. I need to find out just how often he's doing this, because our water does have ~180 ppm here. Thanks!

 

[Texas Splash]

I didn't realize the strength mattered when dosing, so long as you adjust the formula.

You are correct. If someone was to use 14.5% versus 31.5%, the result should be the same if they adjust the dosage. Sounds like you have a good handle on all the concepts. As you noted, perhaps the fill water is the issue.

 

[jesse-99]

Wouldn't an air leak, for example if the pump basket cover of the main filter (suction side) had an air leak, it would cause lots of bubbles visibly inside the pump basket and potentially cause a small amount of aeration and therefore pH raise if the pump was running constantly? I know when one of my pump basket covers had a small air leak (and would drip water out of the cover when the pump was off, but get sucked down when it was on), I could always see lots of air bubbles in it. Maybe it's so negligable it wouldn't raise pH any... Just a random thought. Comments welcome

 

[JJ_Tex]

So the customer is bringing you a sample. Is it fresh and did they make sure it is not rolling around in the back seat and getting aerated on the way to you?

Also, is the customer the one adding the acid? If so, that could be another variable. You wouldn't think it would be that hard to measure out the right amount of MA and add it, but we have certainly seen stranger things happen.

I would also suggest re-testing 30 minutes after adding the MA to make sure it is getting to the desired target.

 

[Bperry]

If there’s a water leak and the skimmers are close to sucking air, a little waterfall can form right into the skimmer which is aeration. Might be something to check.