Acid - Further Reading

Muriatic Acid

Muriatic acid is used to lower pH and TA.

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.

• 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

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

Tips

• 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.
• 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.
• Lowering TA by the 'slug' or acid column method is a myth. TA changes the same no matter how you add the acid.

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 sodium bisulfate. After dissociation of the acid salt, it leaves behind the sulfate ion. Sulfates can damage concrete & plaster as well as 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). Sulfates can only be removed by draining water. While its use in vinyl pools is typically not as problematic as in plaster pools, scaling of gypsum crystals can increase the risk of liner puncture.

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.