Acid - Further Reading

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Muriatic Acid

Muriatic acid is used to lower pH and TA.

Muriatic acid is hydrogen chloride, so you're not adding anything new that's not already in your water.[1]

Muriatic acid degrades to water and salt. Only harmful gas from muriatic acid is when it is in the bottle. It will corrode metal nearby.[2]

Muriatic Acid Strengths

You will find muriatic acid in various strengths. The most commonly found are 15.7% or 31.45%. Although you may find 14.5%, 28.3%, 29%, or 34.6%. Alongside the % strength there may be a Baume (Be) number.

Baume to percent

The °Baume scale is an old antiquated method of measurement of a chemicals Specific Gravity. It was devised a long time ago and is a scaling on a hydrometer which measures the Specific Gravity of solutions. To really make things confusing there are 2 ways of using this scale, one for liquids that are more dense than water and one for liquids less dense than water.[3]

  • Liquids with lower S.G. than water, S.G = 140 / (°Bé + 130 )
  • Liquids with higher S.G. than water S.G = 145 / (145 – °Bé )

So, if you have the °Baume of a known chemical, you could calculate the S.G. From this you can compare the S.G. of the particular chemical and see what the actual %concentration would be.

Example 20° Bé Sodium Hydroxide NaOHSG = 145 / ( 145 – Bé ) = 145 / ( 145 – 20 ) = 145 / 125 = 1.16 If you look at the data of Sodium Hydroxide you will see that a S.G of 1.16 represents a concentration of approx. 15 %

Storing Muriatic Acid

  • Store muriatic acid in a plastic storage unit, if you have kids, that is WELL VENTILATED
  • Store muriatic acid outside in a shady area
  • Never store muriatic acid near chlorine
  • Keep the muriatic acid away from metal as it's fumes can cause rust. So a garage is not a good place to store muriatic acid.

Safety Cautions

  • Wear safety glasses for working with muriatic acid
  • Always pour the MA *into* the water, not the water into the MA.
  • Do not inhale the fumes when handling muriatic acid
  • Handle muriatic acid only once pouring from the jug into the pool
  • Separate adding chlorine and acid by at least 15 minutes
  • Always have pump running and pour by a return
  • It is safe to swim 15 minutes after adding acid

Acid Magic

Acid Magic is basically muriatic acid (unknown strength) that is buffered using proprietary phosphate containing buffers that can, but don't necessarily, breakdown into phosphates. It may also contain a cationic surfactant in it that suppresses fumes.[4]

Acid Magic claims to have:

  • 90% Less fumes
  • Little to no corrosion caused by fumes
  • Can't burn intact skin

Why would anyone pay $13/gal (3 times the price if regular strength MA) for something that is hardly anymore safe to use???

Muriatic acid is not as dangerous as everyone thinks it is. A bottle of bleach can be way more dangerous than muriatic acid.


  • Never pour muriatic acid into a measuring cup; open the jug, float it in the pool, and pour right into the water. Mark jugs with 1/4, 1/2, and 3/4 lines from a stick calibrated once with water, then use that to control how much you put in. It doesn't usually have to be exact.
  • Pour acid slowly into the water. Acid is heavier then water and the faster you pour acid, more of the acid will sink to the bottom of the pool. With a slow pour over a return, more of the acid gets distributed through the water column. Watch to see how fast the acid is sinking when you add it and adjust as necessary.[5]
  • Tilt the jug low over the water when you pour it in. It reduces any splashing and if the jug slips out of your hand it all falls into the water.
  • Use the handle of your pool brush to stir the water after adding acid or you can brush the walls in that area. That prevents any damage that can happen if the acid sunk to the bottom of the pool.
  • "Green" acid is normally about half strength. It costs about twice per effective amount of acid.[6]
  • Lowering TA by the 'slug' or acid column method is a myth. TA changes the same no matter how you add the acid.[7]

Dry Acid

Dry acid can be used to lower pH and TA. However dry acid contains sulfates which will accumulate in the water. Dry acid should not be used in plaster pools or pools with a SWG.

Dry acid is often sold as “pH Minus”.

Dry acid is sodium bisulfate. After dissociation of the acid salt, it leaves behind the sulfate ion.

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.[8]

Sulfates can only be removed by draining water.

Pentair specifically says on page 9 in the IntelliChlor SWG Manual[9] - 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.

Dry acid should be considered only if obtaining muriatic acid is too expensive or difficult to obtain. In some countries, it’s illegal to sell it to the general public. It’s really not good to have in water.[10]

Dry acid can be used in hot tubs since it’s far easier to measure and dose small quantities of a granular substance and the water in a hot tub gets changed frequently. But, in a pool, it’s just not a good idea.

Sulfuric Acid

You absolutely should not use sulfuric acid in a plaster pool with an SWG.

Sulfuric acid use can cause calcium sulfate scale. Sulfates are bad for plaster and SWGs.[11]

Sulfuric acid adds sulfates to your water. It is not recommended. Sulfates build up and will destroy metal and concrete.[12]

Sulfuric acid is far more dangerous than muriatic acid. While the fumes from muriatic acid are a bit harsh on the nose, they are in no way dangerous (your nose has a low odor threshold for HCl). Sulfuric acid can cause rapidly forming burns on the skin with severe and deep tissue damage while HCl can be splashed on the skin and take several minutes before anything is felt. One should always use splash proof eye protection when handling acids of any kind.[13]

Sulfamic Acid

Sulfamic acid is H3NSO3.

Sulfamic acid is used to lift copper stains. The metals are still in the water and you have to drain and refill to get rid of the metals if you can safely do so without floating the pool.

Jack's Magic #2 Copper and Scale Stuff is sulfamic acid, which combines with chlorine to create CC.

Sulfamic acid creates CC. The chlorine substitutes for the hydrogen to form the CC. A single substitution forms monochlorosulfamate. A double substitution forms dichlorosulfamate. The nitrogen is in the -3 oxidation state like in ammonia. So, breakdown is oxidation of the nitrogen to nitrogen gas.

Chlorosulfamates (both monochloro- and dichlorosulfamate) act as antimicrobial compounds. They have been investigated and patented as alternative acidic bleaching agents. So even though the chlorine gets bound to the sulfamate, there is still some residual disinfecting capability.[14]

FC Testing After Using Sulfamic Acid

FC + CC = TC. So when you do the tests, add your FC and CC together and just consider that total number as your FC until the elevated CC goes away.

Sulfamic acid is similar to cyanuric acid in that chlorine will combine with it and reach an equilibrium. The bond is actually stronger than with cyanuric acid. That's why the chlorine registers as CC.[15]

Periodically do an OCLT to detect any excessive organic buildup. As long as you're passing the OCLT, your total chlorine level should be adequate.

It had taken members months of SLAM level FC to clear CCs after using Jack's Magic #2 Copper and Scale Stuff.

Cyanuric Acid

See CYA.

Phosphonic Acid

Phosphonic acid is used as a sequestrant.