Chlorine Lock

[wellioughta]

I just had my pool water tested at Warehouse Pool Supply. Results:
Free chlorine: 10.0 ppm
Total chlorine: 10.0 ppm
Combined chlorine: 0.0 ppm
pH: 7.6
Hardness: 420 ppm
Alkalinity: 110 ppm
Cyanuric Acid: 300 ppm
Copper and Iron: each 0.0 ppm
They tell me I have chlorine lock. I can't completely understand why I have so much free chlorine yet I get yellow algae. This just started to happen (within the last two weeks) and the only difference is I switched to calcium hypochlorite from a stabilized chlorine. If it's true that the very high CYA level is somehow keeping my free chlorine from working, how do I rectify the situation. I'm in a Texas drought and draining my pool is not really a good option. Thanks.

[Watermom]

Hi and welcome to the Pool Forum. The only way to lower CYA is through a partial drain and refill. I'm not sure how they measured yours at 300ppm. Testers typically can't differentiate over 100. At any rate, you are getting algae because you aren't keeping the chlorine high enough. The higher the CYA, the higher the chlorine has to be. Take a look at the Best Guess Chlorine chart in my signature below.

I would suggest not using cal-hypo. Your calcium hardness reading is very high and you may end up with cloudy water problems. A better bet for your pool would be to just use plain, unscented household bleach for your chlorine. If you tell us the volume of the pool, we can help you with dose sizes of bleach.

[PoolDoc]

As Watermom indicated, you need to verify your CYA reading -- and make SURE it's really that high.

If it is, it's probably not practical to run chlorine high enough to compensate for a 300 ppm reading. However, if you can find some granular sodium bromide at a pool store -- products like "Yellow Treat" -- using small careful doses can provide an immediate work around for the high CYA. So, do this:

#1 - Add 3 gallons of plain 6% household bleach per 10,000 gallons of pool water to your pool, ASAP
#2 - Purchase a cheap OTO/phenol red test kit, and use it to maintain dark yellow / light orange chlorine levels (10 - 20 ppm)
#3 - Once your chlorine is that high, brush your pool repeatedly.
#4 - Meanwhile, purchase a K2006 and do a dilution test of your CYA level, mixing 3/4 cup tap water with 1/4 cup pool water, testing the mix for CYA and then multiplying the result by 4.
#5 - Also, look around and see if you can buy a sodium bromide product -- you may need to call a couple of pool stores, and it may be sold as a spa product. Once you find some, add 2 tablespoons per 10,000 gallons of water to start. MORE IS NOT BETTER! And MAINTAIN your chlorine levels!
#6 - Tell us what bromide product you got, and how many gallons you have, and I'll figure a more exact dose.

These instructions should enable you to work out a process that will work till you can replace some water.

[CarlD]

Hi. There's no such thing as "Chlorine Lock"

OK, you want to get your chlorine level up to 25ppm and keep it there! For the moment you can guestimate: add 2 1/2 gallons of 6% regular unscented bleach for every 10,000 gallons of water (that will add 15ppm of FC). So if you have 20,000 gallons add 5 gallons of bleach. If you have 15,000 gallons, add 3 3/4 gallons (ah, just add 4 gallons!). You'll need to have your water tested every day. Keep FC at 25 till the water clears.

You'll want a proper test kit. Click on the "Amazon Links..." in Watermom's signature.

Run your filter 24/7, brush and vacuum your pool to waste every day.

I agree with 'mom--a CYA level of 300ppm is probably a mis-reading, but if you've been using vast amounts of chlorine tablets, having well over 150 is almost certain--and the effects sound right.

Tablets add phenomenal amounts of CYA and people who aren't taught to test their water weekly for CYA levels get into precisely your situation. One must stop using tablets when the CYA level reaches or exceeds a good target level, usually 50ppm (though we have situations where more is preferable).

Stabilizer is a two-edged sword. It helps protect and preserve chlorine by...making it act slower and therefore, less effective.

Carl