SLAM question…

Bvacchiano

Silver Supporter
Apr 6, 2018
362
Sugar Land, Texas
How fast during a slam can you expect the FC level to fall to the SLAM level? Example you think the CYA is 70 but it’s actually 60 (or who knows possibly 50) for an SWG pool. If u raise the FC to 28 how fast would you expect it to fall during the day to 20-24 if your CYA is actually 50/60? Is it rapid? I’m helping a buddy so we are erroring on 28.
other question is when the water gets clear and u r ready to do the OCLT I guess we need to let it fall below 20 before you would do it? (Ie if u raised it to 28 and your CYA was actually 50/60 would FC fall to slam level of 20/24 OVERNIGHT confusing you that you still had algae in pool)
 

mknauss

Mod Squad
TFP Expert
Bronze Supporter
May 3, 2014
44,003
Laughlin, NV
Pool Size
6000
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
Pentair Intellichlor IC-40
Hard to say. With full sun on the pool it will fall pretty quickly (could be minutes, could be hours) depending on organic load,etc.

For OCLT you can let the FC drop below SLAM level some. As long as the FC is 10 ppm or above for the OCLT all is good.
 

Texas Splash

Mod Squad
TFP Expert
LifeTime Supporter
Jun 22, 2014
33,434
Texas, San Antonio/Marion, South-Central Area
Pool Size
17888
Surface
Fiberglass
Chlorine
Salt Water Generator
SWG Type
CircuPool RJ-45 Plus
For your first question, I'm not sure there is one perfect answer. Yes, FC can fall a bit quicker if you over-shoot your CYA-designated FC level. But to try and estimate it would require more than just the FC/CYA ration and all the other factors come into play such as organics in the water, heat, water temp, amount of sunlight, intensity of the sun, etc. But in general, FC over the amount required for teh CYA becomes waste.

As for the OCLT, there have been some cases where those who had a very high FC SLAM level (i.e. 31 or more) experienced more of a drop during the OCLT. No need to let it fall too low though. I agree with Marty, keep it in that 10-20 range and you should have a reliable result.
 
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