I am starting a new pool service and have been studying for about 6 months now, currently working on my CPO.
One thing I am confused about is maintaining proper chlorine / CYA levels with a weekly service.
I understand the need for CYA and I am opening my service in South Florida where the pools run year round.
Using stabalized pucks will continually add CYA while using unstabalized chlorine runs the risk of chlorine levels dropping to low between services.
What is the best way to handle chlorination without running the risk of it getting to low between services while making sure that CYA levels stay in check.
Is the answer partial drain / fill every so often or using the tabs at a minimum and doing weekly shocks with unstabalized chlorine?
Curious how those in the business handle this balance.
Thanks in advance for your advice.
Replies
You have several options and different pool services use different techniques. Here are some of them and combination hybrid techniques are also possible.
Trichlor. For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm. So at 2 ppm FC per day, this would be 36 ppm CYA per month. In the worst case with plenty of algae nutrients (phosphates and nitrates), you would need to have the FC be at least 7.5% of the CYA level to prevent algae growth. The following are techniques for managing the pool as the CYA level climbs:
Chlorinating liquid and/or chlorine gas. You can set the CYA level higher in sunny areas, to around 100 ppm, so that the daily chlorine loss will only be around 15% per day. Then add chlorine to a high level of around 14 ppm FC and when you come back the next week it will probably be around 4 ppm so adding more chlorine will kill off any algae that may have started to grow.
My local pool store which has 2 branches and services over 2000 pools uses Trichlor tabs in floating feeders and have a target FC of 4.5 ppm. When some pools start having problems at higher CYA levels (usually around 80+ ppm), they shock the pool and if that doesn't fix the problem then they use a phosphate remover. When the CYA hits 100 ppm or more they do a partial drain/refill.
A pool service that services over 1000 pools in desert and hot regions uses a combination of chlorine gas and chlorinating liquid at higher CYA levels.
I understand that bather load and other factors will come into play on different pools so this may not be a question that can be answered on in general.
The "Chlorinating liquid and/or chlorine gas" description does not use any Trichlor tabs. It is a method that only uses sodium hypochlorite as the chlorine source (one could use some Cal-Hypo if they wanted to, so long as the CH is managed). One needs the CYA high enough for outdoor pools exposed to sunlight so that the chlorine lasts longer and the FC will swing high-to-low-to-high quite a bit each week, but there are pool services that do this effectively.
Though 14 ppm FC sounds scary, with 100 ppm CYA this has the same active chlorine level as 7 ppm FC with 50 ppm or 4.2 ppm FC with 30 ppm CYA or 0.14 ppm FC with no CYA. It will be a more noticeable amount of chlorine compared to a typical residential outdoor pool, but will be much less noticeable than a typical commercial/public indoor pool with no CYA.
As for whether this approach will work through the week, as you point out it depends on factors such as the rate of chlorine loss from sunlight and bather load (and organic debris blown in, etc.). For safety, one could use an algaecide or phosphate remover with the approach as insurance.