Common Rookie Chemistry Mistakes to Avoid with Chemistry Expert Bob Lowry

If you are just getting started in the pool industry or just bought a home with a pool, there are a few common chemistry misconceptions that you should know about. I go over a few of these in this podcast with chemistry expert Bob Lowry.

Bob Lowry is the author of over 23 books but this has to be one of his most relevant and shortest books coming in at just 19 pages thick. But it is packed with so many essentials on residential pool chemistry that you will want a copy to carry in your service truck. Bob Lowry has been in the industry for over 47 years and is the Lead Consultant at Lowry Consulting Group, leads the Pool Chemistry Training Institute, and has created the Certified Residential Pool & Spa Certification Program. Learn more at

If you are struggling with algae in a pool and the chlorine level appears to be fine at 3 or 4 ppm and you are scratching your head, the answer may be something you never considered. Maybe 3 ppm is not enough to prevent and kill the algae? Yes, it is the industry standard but Bob Lowry has a theory that is supported by 1,000 hours of research that the Cyanuric Acid level (CYA) actually should dictate a pool’s Free Chlorine (FC) level. The magic number is 7.5%. This means for a pool to be free of algae the Free Chlorine level needs to be 7.5% of the CYA level.

How does this math look:
If your CYA level is 50 ppm then you need an FC level of 3.75 ppm so let’s make it 4 ppm. If you have a pool at 50 ppm and you are having algae blooming and the FC is at 3 ppm this means there is not enough Free Chlorine in the pool to kill and prevent algae. Raising it to 4 ppm will prevent algae in the pool.

If the CYA level is at 100 ppm then you will need 7.5 ppm of FC to prevent algae from growing. If that pool is at 5 ppm it will allow algae to grow because there is not enough Free Chlorine in the water.

Another thing to note that if at any time during the week the FC level drops below this mark, algae can form. Let’s say the customer has a pool party on Saturday. The chlorine level zeros out and your service day is Tuesday. That means for 2 days that pool had no FC in it. During those 2 days algae can certainly grow and bloom.

So how do you prevent this from happening? Having a good FC level all week is the logical answer. One way to boost the chlorine is to use borates in a pool to 50 ppm. Borates are a natural algaestat which means it prevents algae from even forming.

With borate at 50 ppm, the formula changes to 5% FC to the CYA level.
So if a pool has a CYA level of 50 ppm you only need 2.5 ppm of FC in that pool each day to prevent algae.

I also think using a mineral technology like a PoolRx is a great way to boost the chlorine in a pool. The PoolRx will kill and eliminate all microalgae in a pool and keep it algae-free.
Pool runtime is also another critical part of this equation. The more you can run a pool the better. If a customer only wants you to run their 20,000-gallon pool 5 hours per day, I can almost guarantee algae will form in that pool. For one, the chlorine will not be circulated effectively and there will be dead spots in the pool – areas where chlorine won’t get to make it ineffective. The pool run time and circulation are one way to prevent algae from forming.

If you keep the pool’s FC level up to the acceptable level and run the pool as much as possible your pool will remain algae-free barring any filtration issues.

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