Quote Originally Posted by Tredge
Are you saying that because the water "between the blades" is 80+ppm chlorine while the water exiting the cell is only 1-2ppm higher than the pool itself that the high CYA acts as a transport of that high chlorine? Sort of a way to get it into the pool?
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In my experience, when I ran my SWG at 80ppm CYA, my chlorine maintained at a lower power setting....as suspected. However, Algae on the walls and in the pool ran out of control and I fought it all season.
Ever since I lowered my CYA to 35-40ppm, I've not had to shock my pool once and haven't had a hint of "slimy walls" or the onset of algae.
I don't believe the purpose of the high CYA is to "transport" the chlorine into the pool, but you are close to what I do believe is the purpose of the high CYA in making the salt cell more efficient. I'm going to try to explain this non-technically, but if I fail I apologize in advance.

The efficiency of the salt cell in generating chlorine is dependent on how much of this generated chlorine already exists near the generating plates. If there is already a lot of chlorine close to the plates that generate chlorine (due to its building up and not getting swept away fast enough), then the efficiency of the process drops and less chlorine is generated. The purpose of the CYA seems to be to combine with the chlorine that is generated and effectively "hide" this chlorine from the salt cell so that as far as the salt cell is concerned, the concentration of chlorine near its plates is not 80 ppm but something much less. The key to making this work is that the chemical reaction that combines the chlorine with the CYA to "hide" the chlorine needs to be faster than the production of the chlorine from the salt cell and it turns out that the critical point where this takes place is around the 60 ppm or so of CYA that is the minimum recommended by the manufacterer of the salt cell.

Your experience with algae is consistent with what I was saying in my earlier posts that Ben's chart is important to follow because the concentration of the disinfecting form of chlorine needs to be high enough throughout the pool, not just in pool water that passes through a salt cell. On the other hand, many people have reported no algae problems at higher CYA and Sean's experience is that those with lower CYA have had algae problems while those with high CYA have not, but that might have been due to the low-CYA cases having such low efficiency of salt cell chlorine generation that they couldn't produce enough FC to kill algae even at the lower level of CYA. At this point, I would say the jury is still out and my guess is that the continual dosing of chlorine from the salt cell is somewhat more efficient and does probably zap more bugs, oxidize more organics, and kill more *free-floating* algae than the manual dosing of liquid chlorine. That said, your experience shows that this greater efficiency of continual dosing from a salt cell is not enough and that you still need to have "Ben's chart" chlorine levels throughout your pool.

I do believe that it would be in the best interests of pool owners if the manufacturers of salt cells would at least consider the possibility that designing salt cells to operate at lower levels of CYA would be beneficial to "the rest of the pool" including pool surfaces where algae can develop (and bacteria can hang out in biofilms). All the salt cell makers have to do is simply increase the area of their plates over a larger volume and drop the power so that the local chlorine generation rates are lower since that will require a lower concentration of CYA to be able to "keep up" and "hide" the chlorine that is produced. And yes, this means that the salt cell may have to be bigger or, most likely, longer than it is today and that means more bulk and more piping to deal with this, but if it means a better situation for pool owners, then that's the right thing to do.

I just want to thank all of you that post on this and other threads. I have never experienced such a wealth and diversity of information and assitance in an environment that has remained civil. It's refreshing!

Richard