Re: Chlorine Locked?
The sodium percarbonate will oxidize the biguanide and goo in your pool. However, it will also destroy any chlorine and chloramines present since it creates hydrogen peroxide when dissolved. Therefore, you might need to dose two or three times with the percarbonate for it to be effective if you have high levels of combined chlorine presently. The first applicaton with get used up destroying the chlorine compounds and subsequent applications can then attack the biguanide and residue in the pool.
Normal dosing is 1 lb per 1000 gallon water and since it will cause the pH to rise the addition of 3/4 lb of dry acid for every 1 lb of percarbonate added will keep the pH in line. So for a 10k gallon pool you would need 10 lbs of percarbonate and about 7 lbs of dry acid for each dose. Turn off the pump and broadcast the perscarbonate on the water surface then immediately broadcast the dry acid. The stuff may 'fizz' and cause gunk to float to the surface.
Skim out as much of this as possible then turn on the pump and filter 24/7 for 48 hours. You should have no or little chlorine in the pool at this point and should clean the filter and repeat the process again.
If the water is not clear after another 48 hours of filtration repeat again.
Some people do not add the dry acid initially and let the percarbonate work at the higher pH then lower the pH after the conversion I do not personally know which method is more effective but do know that it does work either way.
At this point what little biguanide remains in the water and filter should be easily oxidized by chlorine if any is left so add chlorine and see how much CC is present or if the water turns colors when you add the chlorine. Once conversion is complete change out your filer medium, be it sand, cartridge, or DE. NO simple backwash here. Break down the filer and clean and soak everything. Repalce the sand, carts or DE completely.
Do not swim in the pool until conversion is compete. The water can be irritating to say the least!
Retired pool store and commercial pool maintenance guy.
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