Perhaps a cornerstone element of TFPC is understanding the relationship between the chlorine in your pool and the stabilizer you put in to protect the chlorine from the sun. Generally, the more stabilizer (CYA), the more chlorine (FC) you need to maintain its effectiveness. The charts below show the recommended relationship for outdoor residential pools.
| CYA (Stablizer) | Minimum FC | Target |
|---|---|---|
| 20 | 2 | 3-5 |
| 30 | 2 | 4-6 |
| 40 | 3 | 5-7 |
| 50 | 4 | 6-8 |
| 60 | 5 | 7-9 |
| 70* | 5 | 8-10 |
| 80* | 6 | 9-11 |
| 90* | 7 | 10-12 |
| 100* | 8 | 11-13 |
Stablizer levels of 70ppm are not suggested. Users should drain some water.
| CYA (Stablizer) | Minimum FC | Target FC |
|---|---|---|
| 60* | 3 | 4 |
| 70 | 3 | 5 |
| 80 | 4 | 6 |
Stablizer levels of 60ppm are not suggested. Users should add some CYA.
| CYA (Stablizer) | SLAM Level |
|---|---|
| 20 | 10 |
| 30 | 12 |
| 40 | 16 |
| 50 | 20 |
| 60 | 24 |
| 70 | 28 |
| 80 | 31 |
| 90 | 35 |
| 100 | 39 |
The shock levels shown have equivalent effective disinfecting chlorine amounts. At very high CYA levels it can be impractical to reach such high FC levels. At CYA levels over 80, a partial drain/refill to lower the CYA level is usually required before you start the SLAM.
Most saltwater chlorine generator (SWCG) pools appear to remain algae-free at a lower minimum FC level compared with the minimum FC column for manually dosed pools. This may be due to the high chlorine level within the cell.
For indoor pools we recommend CYA between 20 and 30ppm. The reasoning for using CYA indoors is quite different. For more information please ask on the forum.
Acknowledgment: The original Chlorine/CYA “Best Guess” chart was developed by Ben Powell. Richard Falk (chem geek) has refined and expanded on that original to produce the Chlorine/CYA Chart by Chem Geek based on experiences with members on this forum and the old Pool Forum and conformation to chemical theory.
