High acid demand

[jspeacock1978]

Our pool was remodeled over the winter we went with a Wet Edge pebble liner. The pool was filled up on March 26th and the initial startup steps were performed by the PB. I followed the start-up instructions to the letter and 30 days later the PB returned to add salt and turn on the salt system. As expected the pool required lots of acid in the beginning to keep things under control. After the first month, acid demand dropped off significantly but the pool still seems to have a heavy demand for acid. Just over 4 months after the pool was filled I would have expected it to have slowed down. I’ve added over 50 lbs of dry acid to the pool over that time frame and it seems to need 1-2 pounds per week.

I turned off the salt system for a few days as a test but didn’t notice much difference. The goal was to have it off for a week and watch the PH rise, but the PB came back to replace the circuit board for the automation system and turned the salt system back on while I was away on business. I plan on re-running the test in a few weeks.

PH is always measured using a Taylor K-1000 kit with fresh reagents (purchased from Leslie’s < 2 months ago). Seven days ago, I added 19 oz of dry acid, 6 days ago, PH was 7.6, 5 days ago it was still 7.6. 3 days ago, it was up to 7.8 and 2 days ago, it was 8.2. We added 28 oz of dry acid to counter the rise.

The way PH slowly rose and then jumped over just a few days is fairly typical. Most of the time I begin to add acid when it hits 7.8 but on occasion we do let it get up to 8+.

Before we purchased this house my wife and I had a 6000 gallon Intex AGP with a salt system and I only had to add acid twice in the year. I expected after the pebble cured I’d have little acid demand. The guys at Leslies figured I had a leak and my auto-fill was hiding it. His thought was PH could jump from 7.6 -> 8.2 with water adds. He’s crazy - Our water is alkaline (closer to 8.4) but I’d have to replace 1/2 of my pools water for that to happen. I did run a test and turned off the water supply to the auto-fill for a week and the pool was down by ~1” which I attribute to evaporation. Any thoughts?

PoolMath logs:

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[zea3]

You may see pH rise for a full year after fresh plaster, so you are still within that time frame. If you have a SWG you may want to switch over to muriatic acid instead of dry acid. Dry acid has sulfates that will build up and shorten the life of your salt cell. Try dropping the TA to 70 and see if that helps.

 

[ajw22]

Plaster/Pebble pools often have a higher acid demand then vinyl liner pools. Especially if you have a SWG.

Needing to add acid once or twice a week is not unusual on a plaster pool.

We recommend that dry acid not be used as it adds sulfates to the water which accumulate.

Problems sulfates can cause include:

• Sulfates can damage concrete & plaster
• Excess sulfates in water increases the likelihood of corrosion on metal parts
• Excess sulfates in splash out water leads to degradation of any concrete surfaces
• Sulfates degrade the coatings on SWG plates
• At high enough concentrations, sulfates can react with calcium to form spindly, needle-like crystals of calcium sulfate (gypsum)
• While sulfates in vinyl pools is typically not as problematic as in plaster pools, scaling of gypsum crystals can increase the risk of liner puncture.[9]

Sulfates can only be removed by draining water.

Pentair specifically says on page 9 in the IntelliChlor SWG Manual[ - CAUTION: The use of dry acid (sodium bisulfate) to adjust pool pH is discouraged especially in arid regions where pool water is subject to excessive evaporation and is not commonly diluted with fresh water. Dry acid can cause a buildup of by-products that can damage your chlorinator cell.

 

[jspeacock1978]

My first pool was vinyl and the previous incarnation of this pool had a fiberglass overlay on top of the gunite. Neither of these needed much acid if any so I was surprised that after the break-in period I still have such high demand. @zea3 & @ajw22 - your comments are helpful. It does reset my expectations on how long this should keep up. I still worry that the pool is jumping from 7.6 -> 8.2 in 2 - 3 days. Doesn’t that seem excessive especially when the first day sees .2 and the second sees .4.

Is there a way to connect an acid pump to an iAqualink? It would be so much more helpful to have it auto-added as needed throughout the day instead of taking off the cover, adding acid, and putting the cover back on.

The Jandy manual says almost the exact thing as the Pentair manual regarding the use of dry acid. I took this to mean you’d be okay if you keep that pool full. I’d swapped to dry acid when we remodeled the pool so my wife could add acid without needing a full hazmat suite It looks like I’m swapping back to muriatic acid.

 

[KJB1]

My new pool was filled in December and just recently has the acid demand begun to slow down. It is sort of alarming at first. Just give it what it wants

 

[ajw22]

This says you need to add acid about once a week. That is not bad…

Seven days ago, I added 19 oz of dry acid, 6 days ago, PH was 7.6, 5 days ago it was still 7.6. 3 days ago, it was up to 7.8 and 2 days ago, it was 8.2

What is your fill water pH and TA?

Get your pool TA down to 60 and it will slow the pH rise some.