Muriatic Acid versus granular acid

[chem geek]

This is NOT true. Muriatic Acid and Dry Acid will have the same effect on the pool water. The "acid column" or "slug method" were formally debunked here. There is a negligible effect on the way acid is added, but the most efficient way to lower the Total Alkalinity (TA) is to follow the procedure described in the post at the start of this thread. If the dry acid dissolves slowly, then it's effect on BOTH pH AND TA will be slower -- there is no separate effect that somehow the dry acid dissolves only affecting pH and not TA!!!

pH and TA move together when adding acids or bases. However, aeration of the water raises the pH with no change in TA as it drives carbon dioxide out of the pool which ultimately is the ONLY way that TA gets lowered at the same pH level. That is, you can drive yourself crazy adding acid to lower pH and TA and then adding base, or even worse, pH Up, to raise the pH back up and find that the TA is even higher than before!

Remember that TA is mostly a measure of bicarbonate and that this is proportional to the amount of dissolved carbon dioxide in the water (that proportion varying with pH). Pools are intentionally over-carbonated (like a carbonated beverage, though obviously not THAT carbonated) in order to provide a pH buffer and to saturate the water with calcium carbonate (the carbonate coming from TA, the calcium from CH).

The key to a faster lowering of TA is to lower the pH by adding acid, usually to 7.0, and aerate the water as much as possible. As the pH rises, add more acid to keep the pH low and continue to aerate. This process will drive off carbon dioxide and lower the TA level. When the TA level is where you want it, stop adding acid and just aerate to raise the pH to the desired level.

Richard

[Me...]

Heehee A topic that will never go away. I am not sure about dry acid but I do know I will continue to use this so called slug method. Its what I have always done as it always seem to work the way I intend it to work. And it has never caused any damage and ......................... it makes me happy

[chem geek]

Heehee A topic that will never go away. I am not sure about dry acid but I do know I will continue to use this so called slug method. Its what I have always done as it always seem to work the way I intend it to work. And it has never caused any damage and ......................... it makes me happy

To lower TA, you've dumped acid in one spot in a vinyl pool with the pump off? Low pH is the worst thing for wearing on a vinyl pool.

TA will get lowered based on the amount of acid that is added, regardless of how it is added. If you then just wait for the pH to rise on its own from outgassing (that is, do NOT add any pH Up product), the TA stays at its same lowered value so there is a net reduction in TA. It won't matter how you've added the acid. If you add it slowly around the pool, you'll still get the same TA reduction. 7.2 cups of full-strength Muriatic Acid (31.45% Hydrochloric Acid) in 10,000 gallons lowers the TA by 10 ppm.

In other words, adding acid over time lowers the TA anyway so I'm not saying it doesn't work, just that it's not efficient if you want the TA lowered more quickly.

The only purpose of the "lower pH, aeration and acid" procedure is to accelerate the process by increasing aeration and having the pool's pH be lower as a whole so the entire surface of the pool participates in the carbon dioxide outgassing. You don't use less acid with any procedure -- you can only accelerate the process in a kind of "pay a lot now" vs. "pay later over time" tradeoff in terms of when the acid is added.

So are you saying that if you add the acid around the pool instead of in one spot that the pH will drop and the TA will not? It will be hard to see that unless you are dropping the pH a lot since at 100 ppm TA it takes dropping the pH from 7.5 to 7.07 or from 8.0 to 7.27 to see a 10 ppm drop in TA. At 150 ppm TA it takes dropping the pH from 7.5 to 7.17 or from 8.0 to 7.43 to see a 10 ppm drop in TA. Also, I presume with the slug method you are not just measuring the TA in the spot where you dumped the acid but are waiting after turning back on the circulation and then measuring the TA overall in the pool.

Richard

[Me...]

Where I am, Alkalinity comes out of the tap at about 10-20ppm. I do a substantial number of auto feed systems using Liquid Chlorine and Muriatic Acid. I could have people fill their acid vat with straight Muriatic but instead I have them dilute it about 10-1. Put in 10 gallon of water for every gallon of acid. Their systems chug along nicely and the Alkalinity holds pretty steady with of course the occasional addition of Bi-Carb.

Several times either the owner or someone else has advised the owner to just use straight Muriatic. I know when this happens because all of a sudden their bi-carb consumption goes through the roof. And of course they now start to get nice big spikes in their pH readings. As we also know, if the pH is (spiked) low, the ORP reading will be falsely high and even if the pool is wanting some chlorine, the controller thinks it is good enough and won't feed.

When that false low spike is over you can imagine the chlorine demand is now higher and so it feeds more chlorine than in a normal cycle which of course creates more acid now. In the meantime all this acid feeding with straight Muriatic has lowered the TA and when the Bicarb goes in guess what, we have even more pH demand.

Anyways, feeding chemicals in stronger solution than needed can create havoc. The cycle described above is real and happens. Of course some fill water might deserve a stronger solution but this scenario has convinced me that adding it strong (in one place) will affect Alkalinity moreso than adding it weak (pouring it around the edge)

And no, I do not recommend ever adding any chemical to any pool with the pump off.

[chem geek]

OK, that makes more sense. Concentrated chemicals combined with single-point measurements in a feedback system can create havoc so having slower diluted introduction with good mixing is far better. I was more commenting on the manual addition and not saying that there was no difference, but that it wasn't very much and that low pH with aeration was more efficient, especially for lowering the TA by larger amounts. Some people have used air compressors or special attachments to their returns or turn on waterfalls, fountains and spillovers that really aerate the water and it has the process go a whole lot faster (especially if the pH is lowered to 7.0).

One area where one does see a substantial noticeable difference in terms of how chemicals are added, especially in spas, is when adding baking soda to raise the TA. Theoretically, the rise in pH should be fairly low from such addition, but oftentimes one sees a larger pH rise. This is most likely due to immediate carbon dioxide outgassing when the baking soda concentrates the water near the surface where added to be very high in TA and then outgasses carbon dioxide raising the pH.

Richard

[adain24]

sounds so delicious! Thanks


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Nu-Pet Granular Greens

[darryl2]

I just poured 2/3's of a 1lb,6oz bottle of sodium bisulfate to to my above ground pool.It's measurements are 18'x26'x4'.A free water test at a store said my ph was high and chlorine low.And that was all.So I picked some up.I have yet to add chlorine.I have some tablets laying around for the pool,and a 2 1/2 gal container I was going to use for the well water.Did I do this right?

[Guest]

I have never heard of anyone recommending mixing chemicals (acid or otherwise) in a bucket of water before adding to the pool. I would not listen to this recommendation as it is BS.

[chem geek]

The only "bucket of water" reference was in the first post in this thread and that bucket was only being used to mix acid with water. So long as acid is added to the water and not the other way around, then diluting the acid in a bucket of water is OK, though not usually necessary since adding it slowly over a return flow usually provides enough mixing, especially if the pool side and bottom is lightly brushed in the area where it was added.

The part about Muriatic Acid and dry acid behaving differently in terms of TA is bunk, but diluting acid in a bucket of water isnt' a problem. I agree that one should generally not mix chemicals in a bucket (other than dilution with water in the bucket first).

[Guest]

Hi I just wanted to confirm that in my inground pool the muriatic acid did lower total alkalinity and I had to use Baking soda then back to acid , etc. When I use PH down I don't have the same problem. This year I didn't have to use baking soda once until I used muriatic acid. So the first explanation was accurate for me and not BS as stated.

Oh and PH always rises in my pool anyway I have a salt system but total alkalinity did not crash until muriatic acid was introduced.

[chem geek]

No, no, no. Why did you add baking soda? If you have a problem with rising pH, then you do NOT want to raise your TA back up higher. TA is a SOURCE of rising pH through carbon dioxide outgassing. The procedure for lowering TA is described in this post where you will notice that it is a combination of acid addition and aeration at lower pH. There is NO adding of baking soda to raise the TA, even if the TA is below 80 ppm. If your pH tends to rise, as is often the case for saltwater chlorine generator (SWCG) pools, then you want your TA to be lower. If you use 50 ppm Borates in the water, then you can have the TA even lower than 70 ppm because the borates provide additional pH buffering. If you have a plaster pool, you can have the CH be higher to compensate and should also target a pH such a 7.7 instead of 7.5.

The dry acid most certainly lowers the TA just as the Muriatic Acid does, but perhaps you didn't use as much dry acid. If you used too much Muriatic Acid then that would obviously lower the TA more, but outgassing of carbon dioxide would bring the pH up again eventually so the key is to lower the TA level and KEEP IT LOWER. You do NOT want to raise it by adding baking soda.

There are thousands of pool owners with SWCG systems who have significantly lowered the rate of pH rise in their pools and the amount of acid they need to add -- they did this through the combination of lower TA, higher CYA, and use of 50 ppm Borates as described in Water Balance for SWGs.

[Alfonso]

What is the chemistry involved in the action of sodium bisulfate to lower pH in a pool/spa?

[chem geek]

NaHSO4 ---> Na+ + H+ + SO42-
Sodium Bisulfate ---> Sodium Ion + Hydrogen Ion + Sulfate Ion

The solid sodium bisulfate dissolves in water to release hydrogen ions and these lower the pH. You will notice that you get leftover sodium and sulfate ions as a result. Compare this against using Muriatic Acid which is usually 31.45% Hydrochloric Acid which is

H+ + Cl-
Hydrogen Ion + Chloride Ion

So with Muriatic Acid, you don't get sulfates and only get chloride ion (i.e. a component of sodium chloride table salt). If you use a lot of acid and build up sulfates to a high level, then this can become damaging to plaster surfaces.

[Guest]

I would not worry about TA being at 150 as long as your pH is in a good range 7.2-7.6 then all good. You will find keeping your pH in a good range with the addition of acid (dry or liquid) will bring down the TA naturally so having high TA is usually a good thing. One less thing you have to balance in your pool.

[diddlyD]

Mr. DARTH DOUGY, I was ever so pleased to find your well detailed explanation on this subject mainly as it pertains on how to effectively lower PH "without" lowering TA that otherwise would utimatley results in a YoYo cycle effect that's senceless. I can attest to the fact that "Dry Acid" did not lower my TA only my PH and I was done. in fact, my TA actually had a very slight rise 10ppm. My PH has remained stable since for several days now. I would not recommend using Muriatic Acid as the ideal way to lower PH alone. Although Dry Acid costs more than Muriatic Acid you won't spend as much on chemicals in the long run as you won't endure the lowered TA and ultimately spike in PH again and have to add more chemicals on this endless cycle. IMHO, focus on keeping PH balanced as the priority and then TA should be easier to maintain.