You nailed it!
"Chlorine lock" is a term like "dermatitis".
(You tell your doctor, "Doctor, I have red and itchy skin!". And the doctor says, "Ahh, my young (or old) friend, you have dermatitis". That sounds impressive, till you find out "dermatitis" basically means reddened or irritated skin!)
When pool stores say, "you have the dreaded CHLORINE LOCK", what it means is, "We don't know what's going on with your chlorine, but we've found a better way to say that!".
That said, if 6 gallons of bleach disappeared overnight, you DO have a problem! And I'll tell you right away, I don't know why.
That said, I can tell you that similar problems are *usually* caused EITHER by
(a) emerging algae -- but usually not overnight, OR
(b) by something you put in the pool.
So do all these things:
1. Tell us what you most recent test results are, including pH
2. Keep adding 2 gallons of PLAIN 8% bleach EVERY night till this is resolved. (Doing so will GREATLY reduce the risk of you developing a swamp in your back yard!)
3. Give us a list of EVERYTHING you added to your pool in the 2 weeks prior to developing a problem. Exact maker & product name, please.
4. Order a real test kit: http://pool9.net/tk/
5. Run your pump 24/7.
I'm confident we *can* figure it out!
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