Lowering pH with acid

- chemical formula HCl, Hydrochloric (Muriatic) Acid can be used to lower pH in a pool and is the cheapest chemical to use for this routine maintenance task. It is the liquid acid used (diluted 50:50 with water) with Automatic pH Controllers in place of the more expensive Sulphuric Acid

Wear gloves, goggles and a mask when handling HCl and store it well away from any Chlorine compound because if the 2 substances mix (outside of the pool water) they will release Chlorine Gas, which is very toxic

It's a very useful, inexpensive chemical for pool-owners, but care must be taken because it can burn skin on contact and the fumes are very bad for lungs and eyes. It will also burn holes in clothing and footwear

Hydrochloric Acid is the same as stomach acid - so it's clearly not deadly to us fragile humans - but you still don't want to get it on your skin

If you get HCl on your skin flush with clean, fresh water. If it gets into your eyes flush with water for several minutes and then seek immediate medical help

Dosage for pH reduction: -

HCl does not release fumes at concentrations lower than 22% but for pools it's usually supplied at a strength of around 28%; that's the strength that the doses below are calculated for

  • 1 litre of 28% HCl in a pool of 50m³ will lower the pH reading by 0.2
  • 0.25 US Gallons of 28% HCl in a pool of 10,000 US Gallons will reduce pH by 0.2

This chemical is also useful as a cleaning agent around a pool: -

HCl mixed with water in a 1:1 (50%) ratio is used to acid-wash the floor and walls to remove lime-scale and the same strength mixture can be used to Hydrochloric Acid warning labelfreshen pool copings/surrounds and the walls above the waterline

In all cases, rinse with plenty of fresh water once the surfaces are clean

A mixture of 1:9 (10%) is strong enough for cleaning the plates of a Saltwater Chlorinator but reduce this to 1:19 (5%) for cleaning the elements of Cartridge filters or the grids of DE filters

WARNING: - Always add the acid to the water; NEVER add the water to the acid

Hydrochloric Acid  can stain the allegedly 'stainless' steel of pool ladders and handrails so do not allow it to come into contact with these items


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Ken Walker - MyPoolGuru©