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Muriatic Acid

Muriatic acid is a 31.5% solution of hydrochloric acid. It is typically used as a pH buffering chemical. It can automatically be injected in small amounts into the pool recirculation system.

Muriatic acid reacts with the sanitizer, thus counteracting the pH, raising effects of the sanitizer.  It has a pH of approximately 3.  In the pool, it will lower the pH and total alkalinity.

Muriatic acid is typically delivered in 15-gallon carboys.

Handling acid requires gloves, glasses, and aprons.  Heavy fumes are present.

Muriatic acid (hydrochloric acid) is classified as a corrosive.  Muriatic acid is highly reactive liquid acid.  It must be stored separate from oxidizers and in a well-ventilated space.

The maximum allowable quantity of muriatic acid is 500 gallons when stored in an un-sprinklered area.  Where stored in an area with an approved automatic sprinkler system and in approved storage containers, max allowable quantity increases by 100% for each (up to 2,000 gallons). Control areas for muriatic acid that do not exceed quantities listed shall have a 1-hour rated fire barrier separating the room from the rest of the building.

Where the quantity of acid stored exceeds the MAQ, the control area must meet Protection Level 4 requirements per NFPA 1 and NFPA 400 and occupancy classification of H-4. This includes either a 2- or 4-hour fire rated separation depending on adjacent occupancies, 175ft travel distance for egress, and other requirements.

It is CH policy to use muriatic acid on all pools where the total alkalinity in the source water is above 70 ppm.

A threaded fitting should be used for acid distribution and venting from the acid drum to the outside to help prevent corrosion in the acid room.  The acid container should always be a sealed drum/container.

With spas it is sometimes necessary to dilute the acid because it is lowering the total alkalinity.  CH will then use a second vessel and pump it out with a peristaltic pump.  If the acid is diluted, acid should always be added to water to prevent chemical splash.  NEVER add water to acid (there is not a set ratio, but a good starting point is 4 parts water to 1 part acid).  CH does not recommend diluting because we don’t like the operators to handle acid.  If they do choose to dilute, OSHA standards require anyone handling muriatic acid to wear goggles, aprons, and gloves.

Acid Magic should NOT be used as a substitute for muriatic acid, especially for indoor or heated pools.  Acid Magic contains urea which contributes to chloramine formation and poor indoor air quality, and have led to rapid heater failure, specifically with Lochinvar units and their internal heat exchangers and burners.

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