Possible TFP CYA chart discrepancy for SWG?

[durtynacho]

The TFP CYA chart says the recommended CYA level for a SWG pool is minimum 70. The SLAM chart says that the FC level for a SLAM with this level of CYA is 28, and that this level of CYA isn't recommended (due to the high required levels of FC).

Is that 'not recommended' clause just for non-SWG pools? If 70 CYA isn't recommended for regular pools because the FC level has to be so dang high to SLAM (28), I assume the same is true for a SWG pool, right? Having to slam a SWG is going to be expensive, assuming the FC level of 28 is accurate for a SWG.

Would appreciate any input that yall have. Thanks in advance family!

Also, just to clarify, I don't need to slam my SWG pool yet and haven't had to since I got it a month ago, luckily. I am just trying to get an understanding of what it would take in case I need to. I am quite surprised by that, but the SWG has kept the FC levels about 4-5, which has been pretty nice. Gone are the days of adding liquid chlorine every Dang day!

 

[ajw22]

If you scroll down on the chart you find the following:

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.

You can SLAM at CYA 70. It just takes a lot of chlorine and frequent topping off to keep it at 28.

Those are the trade offs of running a high CYA level. If you never let your FC drop then you never need to SLAM and high CYA works fine.

 

[mgtfp]

Is that 'not recommended' clause just for non-SWG pools? If 70 CYA isn't recommended for regular pools because the FC level has to be so dang high to SLAM (28), I assume the same is true for a SWG pool, right? Having to slam a SWG is going to be expensive, assuming the FC level of 28 is accurate for a SWG.

For a SLAM, all pools are the same. SWG - if present - gets turned off, and the SLAM process is the same.

With an SWG, the risk of slipping below min-level is lower because of the regular chlorine production. Not getting around to adding bleach one day because life happened, is not an issue. And target levels with a SWG can be kept lower because of the constant super-chlorination within the cell. Risk for algae outbreaks is much smaller. That's why TFP recommends higher CYA levels with SWGs to make full benefit of the chlorine saving potential.

The target FC for a SWG with CYA 80 is basically the same as target FC for non-SWG with CYA 40-50 - the absolute FC is the same, but with CYA 80 you have significantly smaller UV-losses.

But if you do let FC slip at CYA 80 (which shouldn't happen with an SWG, but sometimes things go wrong - an unnoticed cell failure or a power outage while on holidays) the SLAM process is much harder. You can do it, but a lot of chlorine will be required and very frequent testing and topping up. Not a major problem if caught early and you just have to SLAM for a day or two. But if you have a swamp that needs two weeks SLAMming to clear, you might be better off draining some water to get CYA down before the SLAM. Or you SLAM at half the recommended level, but then a two week SLAM will turn into a four week SLAM - also not much fun.

 

[durtynacho]

@mgtfp

Perfect explanation, thanks so much!

 

[JW1]

Very good explanation

 

[cowboycasey]

I have had 2, 2 day SLAMs in 8 years when the power went off and I missed it.. Once your on TFP for a couple years you will know when your water does not sparkle that there is a problem.. tested and found the issue and SLAMed... taking your FC to 24 and keeping it there takes some gallons of 10%

 

[OHcabanaboy]

Apologies to the TFP folks. I posted a thread on basically the same subject. I must have not been using the right search terms or I was in the wrong section searching.