1-3 ppm FC is not enough for your CYA level of 100 ppm. Your pool will almost certainly turn green, and pathogens will not be killed quickly enough to prevent person-to-person transfer.
Use this chart to determine appropriate FC levels, commensurate with the CYA level:
Pool School - Chlorine / CYA Chart
Cyanuric acid (CYA, stabilizer) holds a reserve of chlorine. CYA is a marvelous chemical for pool management. The science has been well understood for over 40 years. With TFP levels you will not harm any equipment, or any pool finish. These are the levels we recommend:
Pool School - Recommended Levels
You should read this single page explanation of swimming pool water chemistry:
Pool School - ABCs of Pool Water Chemistry
You can break your brain learning all the chemistry behind this, but in a nutshell, CYA holds the vast majority of the free chlorine (FC) in a "buffer" system. The part that does the sanitizing is called Active Chlorine. As active chlorine is used up neutralizing organic contamination, more is released from the CYA to keep working on new contamination. FC just happens to be what we can easily measure.
There are two main forms of active chlorine, one of which does the vast majority of the sanitizing, called hypochlorous acid. Some people call this the "harsh" part of the chlorine. It's the part that dries out hair, causes swimsuits to wear out, and so on.
To understand TFPC, it helps to understand this comparison. A well-run commercial indoor pool using chlorine gas and zero CYA, with 1 ppm FC and 0 ppm CYA has more active chlorine (the "harsh" form of chlorine) than a TFPC pool has when it's up at shock level. If you live in a city, your tap water has more active chlorine than our pool water. When we run at our usual levels, active chlorine is less than 1/10th of the active chlorine in the commercial pool I described.
Why have manufacturers and chemical companies not caught up with this? That's the crazy frustrating question that makes us all work so hard to explain! And it gave rise to the TFP website and forum and many other sources of advocacy for safe residential pools. Some of the problem is indifference and some is probably profit-motivated. If you love hearing about the experience and science behind TFP. This thread is as deep as it gets.
Pool Water Chemistry
But one thing you've noticed already. Your SWG is working better because of all this, and TFPC will get you even further toward lower cost operation of your pool.
Ask questions any time, and I hope you don't mind me over-answering!!
