As a new owner of an in-ground, SWG spa, I spent some time perusing the recommendations in the Pool School area regarding optimal chemical levels. However, the recommended levels in my IntelliChlor Electronic Chlorine Generator manual are considerably different (based upon APSP standards). I would appreciate some insight in the discrepancy. Thank you kindly.
Pool School
FC: 4 - 6ppm
pH: 7.5 - 7.6
TA: 60 - 80ppm
CH: 350 - 450ppm
CYA: 70 - 80
IntelliChlor Manual
FC: 2 - 4ppm
pH: 7.2 - 7.8
TA: 80 - 120ppm
CH: 200 - 400ppm
CYA: 30 - 50ppm
Many of those levels are based on industry practices going back as much as 40 years with little or no basis in real science.
For example, the APSP will tell you all you need is 2-4ppm FC, full-stop. That is completely wrong as the optimal FC level depends on your CYA concentration as CYA both protects FC from UV but, more importantly, acts as a chlorine buffer that substantially lowers the concentration of hypochlorous acid (active chlorine that kills pathogens and oxidizes bather waste) to levels that allow you to swim in the water. If your CYA is too high and your FC is too low, then there will not be enough active chlorine in the water to kill pathogens and you'll get an algae bloom.
As for CYA, your IntelliChlor manual must be an older version. All of the newer online versions of the IntelliCHlor owner's manual has the CYA concentration between 50-80ppm as Pentair has come to realize that SWG's operate much more efficiently at higher CYA levels.
As for TA, again that is based on industry lore. It was believed that metals would be protected when water contained higher levels of carbonate alkalinity as a passive layer of carbonate would form on metal surfaces. That is totally bogus and it's an idea that was ripped off from the water boiler sciences which deals with a completely different type of water system (closed water systems). There's is also the belief by the industry that the higher carbonate alkalinity more strongly buffers the water against pH dropping. That may be true in some circumstances BUT, with any form of water aeration, high levels of carbonate alkalinity will result in increasing pH levels due to carbon dioxide outgassing. Once again, the industry completely misunderstands or ignores the science of water-carbonate chemistry.
CH levels are mostly irrelevant for vinyl pools and, in plaster pools have very wide ranges. My pool has over 800ppm CH and I run an SWG as well...guess what, I NEVER get calcium scale.
TFP Recommended levels are based on science and the experience of tens of thousands of TFPC practitioners. We teach people how to maintain their pools properly by revealing and simplifying the science behind pool water chemistry. We teach our members how to test their own water so they can rely on themselves and we teach our members all about the everyday (and CHEAP) chemicals they can use to keep their pools clean, clear and perfectly sanitized.
Welcome to TFP
Best wishes,
Matt
