Back to School – Substitute Pool Chemicals are like Substitute Teachers – Effects May Vary

Remember when you found out you had a substitute teacher in school? It usually meant an easy day of goofing off and relaxing, maybe even watching a movie.  You probably didn’t learn as much that day as you would have if your original teacher were in class.  Like substitute teachers, substitute pool chemicals may not give you the desired effect.  In fact, when using substitute pool chemicals, the results can cause injury or death if you’re not paying close attention. 

Why would anyone use substitute pool chemicals?  The swimming pool industry was hit with a massive one-two punch in 2020. Not only did the pandemic wreak havoc on manufacturing and supply chain logistics, but hurricane Laura also hit the gulf coast in August 2020. The after-effects of Laura included a fire which burned one of the largest chlorine tablet manufacturing plants to the ground. New plant construction has started, but it won’t be complete until Spring 2022 at the earliest.

The loss of this plant that was responsible for over a third of trichlor chlorine tablets nationwide, meant there would be widespread shortages for the foreseeable future, as well as dramatic price spikes. Many pool service companies and pool owners found themselves searching for alternatives. But substitutes are not always what they appear. Swimming pool chlorine comes in many different chemical formulations, and most formulations are NOT compatible with other formulations, if they were to come into close contact in concentration. Reactions between different chlorine compounds often involve fire and explosions, as well as the release of toxic chlorine gas.

Trichlor chlorine tablets are one of the most commonly used options to chlorinate pools. With this product in short supply, more people switched to other popular forms including: sodium hypochlorite (liquid chlorine, aka bleach), calcium hypochlorite, or salt. Liquid chlorine and salt chlorine generators look very different than trichlor tablets, and use completely different feed systems, making it unlikely that someone would accidentally mix liquid chlorine with tablets for instance. 

However, calcium hypochlorite (cal hypo) is a popular chemical used for chlorinating pools, and comes in three shapes and formulations: granular powder (the most popular and widely known), briquets (second most popular configuration) and compressed tablets (the least common configuration). When formed into compressed tablets, cal hypo looks similar in shape and size to the trichlor chlorinating tablets.

When cal hypo and trichlor are added separately and diluted in pool water, there is not a problem.  However, these two chemicals are not compatible if mixed in concentration. 2021 saw a rise in chemical mixing accidents, as unsuspecting consumers (and some pool care novices) put cal hypo tablets into trichlor tablet feeders with disastrous consequences.  The two chemicals heat up rapidly when combined in concentration, causing fires, explosions, and melted, damaged pool equipment. Injuries occur when chlorinators explode and from inhaling the fumes created when these two chemical compounds mix in concentration.

How did this misunderstanding happen? Some online retailers looking to make money off the nationwide shortage of trichlor tablets have been selling “chlorinating pool tablets” online to customers who thought they were getting their usual trichlor product, but in actuality received cal hypo tablets.  Although the packaging showed that the chemical was cal hypo, not trichlor, some consumers and pool service personnel did not notice and put them into their trichlor feeders causing incidents like the one pictured below.

Most cal hypo tablet manufacturers started adding a blue dye to their tablets years ago so it would be more obvious it is a different product than trichlor, which is white. Unfortunately in some cases that wasn’t enough, as customers rushed to add the chemical to keep their chlorine level up but suffered adverse reactions. Looking closely at the photo you can see blue chemical residue coming out of the melted trichor feeder, providing a telling clue as to what happened.

A second but less problematic case of substitute pool chemicals became prominent this year when many pool service professionals began using sulfuric acid (sometimes called pool acid) in lieu of muriatic acid.  In the middle of the 2021 pool season there was a sudden and severe shortage of muriatic acid, due to raw material and packaging supply chain interruptions. Muriatic acid is essential for balancing pH, surface cleaning, acid washes, and equipment maintenance.

Sulfuric acid is an acceptable substitute for lowering pH, and has the beneficial feature of being non-fuming, whereas muriatic gives off noxious fumes.  Unfortunately, sulfuric acid is ineffective for acid washes and equipment cleaning. In addition to being less potent, sulfuric acid adds sulfates to the pool water, which can damage some metal components and lead to erosion of stone and cementitious surfaces when sulfate levels exceed 300 ppm. In most cases it would take some time to achieve this high level of sulfates.  Therefore, sulfuric acid is a viable short-term substitute for muriatic acid to balance pH, but best not used long-term.

Just like trichlor and cal hypo, these two acids should NOT be mixed together in concentration, or toxic fumes will be created. Sulfuric acid should not be poured into muriatic acid containers, and chemical feed equipment should not be used interchangeably. These two acids are not compatible in concentration. 

In summary, be extra cautious when ordering and using pool chemical supplies. Read labels and product descriptions closely to understand chemical compatibility and reactivity.  Store pool chemicals apart from each other if they are not compatible, to avoid any accidental spills or leaks that might result in a strong chemical reaction. Understanding your options and following good practices like this will keep your swimming pool operating safely!

By Craig Sears, President, Sears Pool Management Consultants, Inc.         August 2021

Craig Sears

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