Why chlorine/stabilizer targets different for SWG pools?

[algonquinforestpool]

Hello,
I'm still a relatively new pool owner and don't completely trust myself yet so I do get help from the pool store guys on occasion. I'm just curious as to why pool stores recommend a chlorine level of 1-3 ppm and stabilizer of 30-60 for salt water pools while TFP recommends 4-6 chlorine and 70-80 stabilizer. Why do SWG pools need higher chlorine/stabilizer compared to non-salt pools? What are the risks of running lower chlorine/stabilizer over time? My pool is quite shady, just gets sun in the peak of the day for a few hours - would this allow me to keep lower levels? My pool has only been open for 1 month so far this summer and it's typically at 2 ppm chlorine and 45 stabilizer and it's been crystal clear and no issues. Just want to make sure I understand this fully before I increase chemicals. Thanks!

(This morning an hour after adding acid)
FC 2.0 ppm
PH 7.4
TA 80
CYA 45

 

[jblizzle]

First, pool stores have no idea what they are talking about because they typically ignore the FC/CYA relationship that has been well documented from the 1970s. So just ignore what the pool stores or the pool equipment manufacturers recommend in regard to FC and CYA levels.

SWGs are slow to add FC to the pool. Higher CYA levels protect more of the FC from the sun. So, even though the FC level required at higher CYA levels is higher, in fact fewer ppm of FC are lost to the sun, so the SWG does not have to generate as much FC everyday.

If you have a low sun exposure, then you could likely keep a lower CYA level. BUT, for a CYA of ~50ppm, a FC of 2.5ppm is the absolute MINIMUM for a SWG so you are flirting with disaster. Bump the SWG output up a bit and try to keep the FC above 3ppm.

 

[JoyfulNoise]

First off, you've got to ditch the pool store. I know you're new and you feel like you're flying blind but the pool stores will rob you blind. You have the best available test kit on the market (even pool stores use Taylor kits) and you have this site....it's all you need.

As for why SWG's have higher levels and higher stabilizer, it's because it benefits the SWG cell life. I won't get into all the technical details (you can read all about the chemistry aspects of it here - Pool Water Chemistry ), but running at a higher CYA lowers the overall lose rate of FC so your SWG has to work less. It's counter intuitive but you'd definitely think that running at lower CYA and lower FC means you use the cell less, right? Wrong. When your CYA is lower, your daily lose rate of FC is higher which means the cell must run longer each day to make up for the lost chlorine. The FC baseline is higher, but that is because you must maintain a proper FC/CYA ratio. You can set your baseline levels using liquid chlorine and then let the cell maintain it for you. We teach that all pools must be managed with an appropriate FC/CYA ratio as that is what drives sanitation. If the FC is too low and CYA is too high, then there is not enough active chlorine in the water to sanitize and you get an algae bloom. Pool stores still cling to the outdated and unscientific industry standards which say that all you need is 1-3ppm FC full stop...they do not take into account how CYA buffers chlorine and lowers the active chlorine (hypochlorous acid) levels.

So, in the end, if you follow TFP Guidelines, you'll have a trouble free pool. If you follow pool store advice, your pool will be relatively trouble free for a while, maybe a season or two. Then the problems will start and you'll be trapped in the ever expanding cycle of green water and expensive pool store chemicals.