by Rob Cox, December 28, 2017
The topic of the day came from an Ask the Expert question which I monitor - from a pool owner named Joe, having trouble with the build-up of cyanuric acid levels in his pool. Joe wanted to know about chlorine that was not stabilized, not our beloved 3" chlorine tablets and sticks, but chlorine that does not contain cyanuric acid, also known as stabilizer or conditioner.
For every chlorine tablet that dissolves in your pool, a small amount of cyanuric acid also dissolves into the pool water. For most pools with adequate rain, backwashing and winter pump down, it won't build-up to a high level. However in pools that are covered, indoors or with cartridge filters, and in dry regions with little rainfall, cyanuric acid levels can rise too high, too fast.
And when the cyanuric acid level creeps up too high, in the 80-120 ppm range, it can be hard to maintain a good chlorine level, and the killing power of chlorine is suppressed. So pool owners like Joe are told to reduce the cyanuric acid level, by draining and refilling the pool. Bio-Active can also be effective in many cases but not all, to lower cyanuric acid levels in pools.
Here's some other alternatives to replacing the water, or treating with a remover.
Regular bleach, or sodium hypochlorite - contains no cyanuric acid. Household bleach is normally a 5% or 6% strength, while commercial strength bleach for pools is generally 12.5% strength, and delivered by truck and hose. You could add liquid chlorine from a gallon bottle every day, but to avoid peaks and valleys in chlorination, use a Chemical Metering Pump to inject the liquid chlorine directly into the return line, slowly throughout the day. You could use a gallon bottle, but a 5-gal or 15-gal drum (or the 55 gal Vat) is more convenient, set on the ground below a wall-mounted liquid chlorine pump, which pulls the bleach out of the container and pushes it into the return line via hose injection fitting. Chemical pumps are adjustable, in seconds of run time per minute, turning on/off to maintain the setting, but they are constant run. A plug-in timer can be used, if you don't run your filter 24/7. Requires care with the handling and storage of bleach, and the very high pH which will require frequent additions of pH decreaser. Pumps and hoses also require some measure of upkeep, or repairs to hoses and fittings.
Salt Chlorinators, aka salt chlorine generator will create most of the chlorine needed for your pool. Add several hundreds pounds of pure pool salt, and plug-in the controller and salt cell to make the magic. The salt cell will create chlorine instantly in the pipe from plain old salt + h2o, and after the chlorine is spent, it reverts back to salt + h2o again. Salt Cells need some repair or replacement parts every 3-5 years, but in the long run a salt system can cost around the same as the cost of using tablets. But of course, like using liquid chlorine, no stabilizer is added to the chlorine that your salt system creates, although maintaining a 20-40 ppm CYA level is recommended for most outdoor pools. People also like the ease of use of a salt system, and the soft silky feel of the water. The main downside to a saltwater pool is the initial cost of the salt water systems, and the 5 yr (+/-) life on salt cells, sensors, circuit boards and such. But the chlorine, that's hands free and easy to control with push button simplicity.
Tablets made out of calcium hypochlorite, a similar formula to the cal hypo pool shock that we sell, but pressed into 1" tablets. Cal hypo tablets cannot be used in a regular 3" Trichlor tablet feeder, because they dissolve too rapidly. Cal Hypo feeders are used to spray individual tablets with water, slowly one at a time, to release the non-stabilized chlorine into the return line. Like Cal Hypo shock, Cal Hypo tablets are unstabilized chlorine tablets, containing no cyanuric acid. Cal Hypo tablets are more expensive than regular tablets to buy, and the specialized feeders required to use them are also on the pricey side. For pools in hard water areas, Cal Hypo tablets will add calcium to the water, in about the same amount as Trichlor tablets add cyanuric to the water - so you may be trading one problem for another.
There is a fourth method or alternative practice, which may work for some, and that is to reduce the amount of stabilized chlorine tablets used, by reducing the chlorine demand. This can be done by augmenting or supplementing your chlorine with a Nature2 Express or Frog Mineral system, along with regular pool shock treatments, good water balance and good filtration practices. With Minerals, you can use 50% fewer tablets, just enough to produce a low 0.5 ppm level of free chlorine. Most people cut their chlorine tablet usage in half when using a mineral purifier! For example, if your pool uses 4-6 tablets per week, you will only need 2-3 tabs per week, which slows the build-up of cyanuric acid by 50% - which can be enough to alleviate the problem for some pool owners.
Take the fourth method above, and add another alternative sanitizer like Ozone or UV purifiers to the mix, and you can stop using chlorine tablets altogether. When you add the 1-2 punch of a Mineral System + Ozone or UV Systems - you don't need to use any tablets at all. It's true - any clean pool with good water balance and a large effective pool filter, and regular shocking (either non-chlorine or chlorine shock), can use a Minerals + Ozone, or Minerals + UV combination to replace the need for stabilized chlorine tablets. Additional helper chemicals like Clarifiers or Algaecides or Enzymes can also be employed if needed.
There you have it Joe - 3 types of "unstabilized chlorine" or chlorine without cyanuric acid, and 2 alternative practices that can be used to help the problem with cyanuric acid build-up in pools. All of these methods are tried and true, and can be safely and effectively used in most residential inground pools, with good filter systems.
Some are more convenient than others, and all have a significant initial cost to switch over to using non-stabilized chlorine. I hope this helps those who struggle with high cyanuric acid levels.
Thanks for the question, Joe!