Best Guess vs. Aquarite (CYA and FC)

Ok, the manual for my Aquarite says CYA 80 and FC 1-3.

The best guess chart says FC 5-20 with the CYA that high.

I've gone 1 season with the Aquarite recommendation and the other with the best guess chart. I didn't have problems either way, but wondering why the big difference and what everyone else is using?

33k, vinyl pool.

thanks!

Most users with SWG systems are able to use 70-80 ppm CYA with 3 ppm FC, but I would not go below 3 ppm FC. Some users that maintained lower FC got algae. Even two users maintaining 3 ppm FC got algae, but it was mustard/yellow algae. One user got green algae at 3 ppm FC. Everyone else had no algae.

The high chlorine level between the SWG plates (about 80 ppm FC) kills pretty much anything that is free-floating and going through that part of the SWG cell. Though it takes more turnovers before most of the water gets through that "high chlorine" part of the cell, this seems to be enough to keep most algae away. The problem is that this does nothing for any algae stuck in bio-films on pool surfaces. Regular brushing may help in that case.

So generally on this forum we recommend keeping the FC at a minimum of 3 ppm FC if you are using an SWG with 70-80 ppm CYA, but if you want to play it safer or are in an area that is susceptible to mustard/yellow algae, then you can maintain a higher 6 ppm FC.

Richard