Chlorine Block?

[PoolDoc]

"Chlorine lock" is a pool industry term, with no specific meaning, which functions as an all-purpose official stand-in for "We don't know what's going on with your pool".

It's sort of like when you go to the doctor, and say, "Doctor, my skin is irritated" and he says, "Yes, ma'am, you are suffering from dermatitis, and here's some cortisone." Dermatitis just means irritated skin . . . but you already knew that; chlorine lock just means your chlorine isn't doing what the store expects . . . and you already knew that, too!.

Of course, it is possible that you've got some chlorine that's 'weak'. However, in 20+ years in the industry, I've never had that happen to me.

I'm guessing you may have a huge chlorine *demand*, which just means that there's something -- I don't know what -- that's consuming, or reacting with, the chlorine in your pool. One common possiblity, with newly opened pools, is that you had lots of stabilizer last year, and now have none due to biodegradation. When bacteria 'eat' your stabilizer, they 'poop' out ammonia and urea. Sometimes -- but not always -- other bacteria then 'eat' the ammonia and urea, and poop out nitrogen gas. If the biodegradation goes all the way to nitrogen gas, you lose the stabilizer, but have no residue. But, if the process stops with the ammonia and urea, you STILL lose the stabilizer, but end up with the ammonia and urea in the pool.

And guess what? It takes HUGE amounts of chlorine to destroy the ammonia and urea.

One other indicator is the fact that your test results showed chlorine. By any chance, were you using a test (OTO drops??) that shows *total* chlorine? If so, you would have showed the 'combined' chlorine that forms when chlorine is trying to destroy the nitrogen compounds, but the free chlorine test used by the dealer would have showed nothing.

Here's what I recommend:

• If you have an OTO chlorine test, use it, and post the results. OTO does NOT go bad! If you don't have such a test, spend $5 and get one from Walmart, Kmart, etc.
• Get your dealer to test your stabilizer and tell you what the results are. If you had a bunch last fall, and none know, that's a pretty good clue.
• Get 10 gallons of bleach, and dump them into the pool in the EVENING. Be sure the pump is running. Wait an hour, and then test with OTO. If you get a reading with OTO that gets darker with time (over a 10 minute period) that's another indicator.

Assuming the problem is what I suspect, the solution will be repeated doses of bleach. The 2,000 lbs of shock your dealer suggested is ridiculous. If you want to know how much bleach it will take, you can test and see.

• Take a glass or stainless mixing bowl fill it with one gallon of pool water.
• Add 1/2 teaspoon of 6% household bleach. Stir with a plastic or stainless utensil and allow it to sit for 4 hours. Be sure that it is NOT exposed to sunlight. Then use your OTO test to test the water in the bowl; if you the results show 3 ppm of chlorine instantly, you are good to go. If not, repeat doses and 4 hour waits till you DO have 3 ppm.
• Each 1/2 teaspoon dose amounts to approximately 40 ppm of chlorine; on your pool that would be 20 gallons of 6% bleach*

If you don't want to test, but have good indication that it is just stabilizer 'residue', repeated 10 gallon doses should clear it up in a week or so, at a fraction of the cost of the dealer's chemicals. But, be SURE to add the bleach late in the evening. Otherwise, you'll lose it to sunlight before it can react with any urea.

Of course, if you have a concrete pool that can be safely drained, and cheap fill water, it might be easier to drain and refill. But, probably not.

Best wishes.

Ben "PoolDoc"

* I think I got the math right, but feel free to check. I used the following factors:

• 768 tsp / gallon
• 8.345 lbs / gallon water
• 9 lbs / gallon 6% bleach (this may be high)
• 0.54 lbs Cl2 equiv per gallon 6% bleach
• 30,000 gallon pool (estimate -- high if no deep end)