SWG and chlorine levels

[doriec]

Thanks Pat, Poolsean, and Richard. I think I've got the algae licked. The FC fell from only 17.5 from 20 FC last night, no algae is visible, the "bubble colonies" clinging to the sides are gone. and the pool is crystal clear. I am running the SWG 2 more hours each day to see if that helps. My goal is 5 FC. My question is, how can people get by with a FC level of 3.5 when the CYA chart says to run it a 5 FC level minimum? Dorie

[chem geek]

Dorie,

That's a question of hot debate at this long thread. The general consensus is that an SWCG does a better job than manual dosing chlorine because it is doing so more continuously and also has a region in the salt cell at very high chlorine concentrations "shocking" the water that passes through it. There is anecdotal evidence that more people with SWCG systems have less problems with algae than those that don't, though interestingly a couple of people have been reporting algae problems in their SWCG pools just this week.

What is not clear is whether it is OK to operate at a lower FC level. Certainly the continual dosing would allow one to operate at the "min" of the range since the range is there partly to allow for adding chlorine that gets used up each day. The SWCG is better able to maintain a constant chlorine level.

As for the shocking effect, it is also not clear that this is very much different than what happens when you add liquid chlorine (or bleach) to your pool since it first hits the water at extraordinarily high concentration and then diffuses. So again, it is the continual shocking (albeit of a small volume of water) that is probably the main difference.

I certainly would not operate in the recommended range of 1-3 ppm at 70-80 ppm -- at least not anything below the 3 ppm of that range. It's safer to go with 5 ppm, but we simply don't have enough data to make a definitive choice. It's too bad that the SWCG manufacturers have not made their cells operate at lower CYA levels since that would allow for the best of both worlds -- low FC with higher disinfection and algae prevention capability.

Richard

[tphaggerty]

I think the SWG and algae issues come from running too close to the 'edge' of lower chlorine. This is what I did at the start of the season, trying to keep my FC at around 2 to 3ppm. Every time it rained or I had a large bather load, BAM, cloudy water (fortunately resolved with good 'ol bleach).

Now, I have upped my CYA to 60-70 range and keep my FC at about 4 -5 ppm. No problems for the last 8 weeks even with large bather loads and/or rain and blown in stuff.

I think using a SWG involves thinking a little different. The chlorine "trickles" in as opposed to RUSHING IN as happens with a shot of bleach. Regardless of CYA, keeping the FC a little on the higher side keeps a reserve available to tide the generator over for when the immediate demand is higher (or much higher) than the cell can generate. Sort of like having a holding tank for a low volume well.