Salt coversion pool systems, what harm will adding a cup of muriadic acid per 10,000 gals. per week to skimmer intake cause.

I maintain a Florida based pool for testing my product's cleaning ability on the pool cartridge filter. The Pool was 6-months old when I took over the maintence. It has a salt conversion system and is a 10,000 gal. Masonary inground pool. for the first 6-months I found the chlorine level would vary greatly from week to week. The chlorine count would jump from the 2800 -3200 norm to low (no reading signal) then I would Make adjustments and it would jump way high. I was cleaning the electrodes as often as every 2-3 months and they would be loaded with build up (calcium?). Anyway a local 30 year pool guy told me to add 1 cup of muriadic acid per 10,000 gals of water directly into the active pool skimmer if the reading is below 2800 each week. If at or above do not add. I have been doing this for about a year now and have found that the pool stays at around 2800-3200 count and I seldom add salt anymore unless we get alot of rain as the pool has auto refill with only 1/2" swing between normal and the out flow drain so the salt can get depleted quickly from run off. I checked the electrode after one year and have found it tobe in like new condition with absolutly no build-up on it. So I got in an arguement with another pool service guy who told me that adding the acid directly into the skimmer would distroy the pump and other system components and thought this tobe a rectless act. I have seen no problems with the system as yet and the pool is a breeze to maintain. What am I missing; is their some hidden problem /issue that will arrise further down the road that I have not seen as yet?

Replies

Mark A Schreiber October 18, 2011 at 1:21pm

Hi all, sorry that I have not responed quicker to some of your input. I checked the electrodes and after one year of my acid treatments the electrodes were like new not a speck of build-up. I have not found any sign of corrosion and or leaking seals. I did test the water with a smart test strip and free clorine was 1 slightly low, alkalinity was 100 dead on and the ph was 7.5 also dead on. I do add all clear products from time to time as well. Cyanuric acid to stabalize the clorine and calcium cloride to increse harness which I believe protects the masonary. I agree that the 2800 count does sence the salt but before I used the method I first described I found that everything was so unstable. The electrodes would need cleanning often and the salt read out would spike hi one week and crash the next evn though the salt level was fine. Not sure why but with me reading the salt count and adding acid when it dips below 2800 and not adding acid when it is above 2800 all is well in the world! I am not saying that constant vidulance and testing would not yield the same result but this method method with testing every couple of months seems to work great. i take a sample into the pool store and they do the intense testing to make sure all is well.

I see Rex is doing the meet and greet at the Vegas Pool and Spa show. I hope to attend and if any of you guys are there I will be in booth 1334 the Mi-Way In / Aqua Comb booth and would love to meet you face to face! I will have Tal Milligans Multi-Tork products on display as well. Tal is a great friend who got me on this site and he has teriffic product which I do not recieve any monies for promoting.I just really like the guy. Tal will be in the Lass Ind. booth so stop by and see him as well!

Thanks all for the input on my pool issue
Hank Graham October 18, 2011 at 4:39am

I believe that your freind suggested adding acid through the skimmer as his way of "auto-cleaning" the salt cell as opposed to adjusting the pH although you sort of kill two birds with one stone using this method. Other posters are correct in stating that you are inviting seal damage but you say that you have done this for a year without consequence so you make the call on the potential damage. Seals and Cupro-Nickel heat exchangers may not exhibit expensive damage until it's too late. Now, back to the basics, you are really treating a symptom (excessive scaling) not the cause. I would suggest that you read up on the saturation index and practice truly balancing your water. With properly saturated water, staining and scaling should be non-existent. Another poster indicated that salt systems inherently raise pH levels and this is true due to the by-production of Hydrogen in the electrolisys process (the foamy bubbles emanating from the cell during chlorine production). With this in mind, weekly pH corrections are in order to maintain the saturation index level.
David Rockwell October 17, 2011 at 7:24pm

Adding ANY chemicals as a matter of practice, as opposed to adjusting the water chemistry based on the results from a test kit is incredibly risky to the pool equipment (especially if a heater is involved), and to the pool surface and possibly the bathers as well.

While adding a small amount of acid through the skimmer may not cause immediate damage, I'm not sure what good it's doing either. Depending on the hydraulics of the pool the water is moving through the pipes at a rate of 5-10 feet per second, if a salt cell is 1 foot long, we're talking a very short time for the acid to do anything.

You may get away with agressive treatments for a period of time, but I believe that you will see negative results from this over time. Why not just take that cup of acid, dilute it, and use it to clean the cell according to the manufacturer's directions?
Richard A. Falk September 26, 2011 at 6:40pm

I would not add acid directly to the skimmer for the reasons noted in the previous posts.

If the Calcium Hardness (CH) is high or even just to reduce the rate of pH rise, you should lower the Total Alkalinity (TA) to around 70 ppm. That should significantly lower the rate of pH rise and the amount of acid you need to add and should also reduce the amount of scaling in the salt cell. You lower the TA by a combination of acid addition with aeration. Adding it in one place or another doesn't make any difference since 25-1/2 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in 10,000 gallons will lower the TA by 10 ppm no matter how you add it. See how to Lower Total Alkalinity. A chart that describes the process is also here. You should generally add acid slowly over a return flow in the deep end with the pump running and, especially for vinyl pools, lightly brush the area where you add the acid to ensure thorough mixing.

In addition to the lower TA, you can use 50 ppm Borates in the pool which will act as an additional pH buffer particularly strong at preventing a rise in pH as this will reduce the likelihood of scale forming in the salt cell. See this post for more info on using borates. The least expensive approach is to use 20 Mule Team Borax and Muriatic Acid though the easier (though somewhat more expensive) approach is to use Boric Acid such as from The Chemistry Store.
Bruce Wettstein September 24, 2011 at 7:39pm

I believe that your reading of "chlorine" at 2800-3200 ppm was really for salt. It would be nice to know what the chlorine reading is, but I would be more interested in the calcium hardness level and the pH. These two lead to fouling of SWCG cells, and if they are in line you would not need to be dumping acid in the skimmer at all.

Can you post up calcium and pH? I'd be interested to see where that is at.

-Bruce
Kevin Misley September 23, 2011 at 1:06pm

With any salt system you will most definitely see an increase in your pH and your Total Alkalinity because of the higher "basic" value of of sodium hypochlorite.

Weekly additions of acid are sometimes necessary to regulate those chems. On commercial sites acid is introduced on a daily basis through chems readers and feeders.

Check your fill water too for minerals such as calcium. That can drive up ph and TA. Don't forget about cyanuric acid for stabilizing.

I for one do not like to add any chemicals directly thorough the skimmer. Not only is it bad for say impeller seals, but also for heat exchangers and any other rubber seals/gaskets and components downstream. If you have an in-line chlorinator you may have a potential disaster with a high concenetration of acid mixing with tabs-BOOM!

I always adds chems around the perimeter of a swimming pool. Dry chems such as cal-hypo, I pre-mix in a bucket of the pool water and add accordingly making sure all the granules are dissolved.

The acid can be diluted in a bucket also and added the same way.

I find adding the acid around the perimeter adjusts the pH. Adding in the deep section seems to adjust the TA.

This was explained in a Pool and Spa Magazine article years ago (20?) relating to adjusting pH and TA. Honestly forgot the explanation why but it works for me. Might still have article in my archives.

Good Luck
Rob M September 23, 2011 at 9:54am

Dumping acid into a skimmer will shorten the life of the impeller but but you're not adding much, and so long as you only do it once a month or so, it shouldnt be too big of a deal