How long should I leave the cover off of the spa after adding chlorine to maintain the residual level and how long do I leave it off after shocking?
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Volatile outgassing, eh? I think that's sounds reasonable but you'll have to make an appointment with one of our resident chemists if you want a more precise answer! (Sometimes they make housecalls to visit the symbol-challenged!)watsocl said:I have been told that when you shock, you should leave the cover off so that the CC's can escape into the air. With the cover on they just oxidize then fall right back into the spa. Not sure if this info is correct.
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polyvue said:Volatile outgassing, eh? I think that's sounds reasonable but you'll have to make an appointment with one of our resident chemists if you want a more precise answer! (Sometimes they make housecalls to visit the symbol-challenged!)
Indoor pools always seem to have issues with accumulation of chlorine byproducts so I've seen suggested here several times that when shocking one should use electric fans to push the miscreant gases outdoors. It would follow then that removing a spa cover could accomplish the same thing. When I shock my pool I don't leave the solar cover in place -- it comes off until the high chlorine level comes down to about 10% of CYA (the CYA level in my pool is typically 50 ppm, so I replace the cover when FC gets down close to 5 ppm.) Solar covers can withstand more abuse than a flimsy solar cover but you probably don't want to lose all that heat, right?
BTW -- Welcome to the forum!
watsocl said:How long should I leave the cover off of the spa after adding chlorine to maintain the residual level and how long do I leave it off after shocking?
Thanks
chem geek said:At hot spa temperatures, most of the oxidation of bather waste should take place within an hour, though you can check the FC and CC levels to be sure (the CC will rise very soon after adding chlorine after a soak, but will then drop along with FC as the bather waste is oxidized). The most important thing is to add enough chlorine -- many people don't add enough. You'll know you are adding enough if you measure at least 1-2 ppm FC before you next soak (the next day). A rough rule-of-thumb applicable when there is no ozonator is that every person-hour of soaking needs around 5 fluid ounces of bleach or 3-1/2 teaspoons of Dichlor or 7 teaspoons of non-chlorine shock (43% MPS).
If you are using enough chlorine and always maintaining a chlorine residual (except possibly during your soak), then you should not need to shock the spa on a regular basis. I assume you have read the Pool School article on using chlorine in your spa which is otherwise known as the Dichlor-then-bleach method. If you instead use Dichlor-only, then there is more need for shocking and the water won't last less than half as long as when using the Dichlor-then-bleach method.
Richard
BC said:I always thought the purpose was to help keep the cover's liner from pitting due to the initial heavy concentration of chlorine. (My previous tub's cover did this which caused flakes dropping into the tub)