How to kill algae despite 150+ PPM CYA?

Chlorinating, maintaining the right chlorine levels,
chlorine problems. Dichlor, trichlor, cal hypo, bleach,
granules, chlorine pucks and chlorine sticks.
hard8hopping
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My Pool: 15000 gallon, rectangular, in-ground, plaster
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How to kill algae despite 150+ PPM CYA?

Postby hard8hopping » Tue 09 Jun, 2009 02:34

Can someone please help me with this problem? My pool has an algae problem which I tried fixing with Leslie's Chlorbrite and 3" tablets. It didn't work and I subsequently tried using their Green2Clean and Power Powder Plus which helped just a little. Switching to a new strip test kit, I saw the the CYA is above the recommended level - probably from all that Chlorbrite I've been using! It's looks to be over 150ppm. I recognize that this needs to be lowered. Water is expensive in Los Angeles right now, so I hesitate to heavily drain and refill. Is it possible to first kill the algae despite the high CYA level and then slowly reduce the CYA level? If so, how? Simply add liquid chlorine or more Power Powder Plus (i.e. unstabilized chlorine) until there is sufficient free chlorine to kill the algae? And I should probably remove the 3" tablets (also from Leslie's) from the floating dispenser until the CYA is lowered, right? Thanks for your help!

BTW, Leslie did a water test 2 days ago and reported all pH, alkalinity to be normal and free chlorine to be a bit low. Phosphates were also low. They did not test for CYA. I've also cleaned out the filter and been running the pump continuously for days.


chem geek
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How to kill algae despite 150+ PPM CYA?

Postby chem geek » Tue 09 Jun, 2009 03:08

Yes, Leslie's Chlor Brite is Dichlor so for every 10 ppm Free Chlorine (FC) you added, this product also increases the Cyanuric Acid (CYA) by 9 ppm. This is probably one of the most irresponsible products on the market when sold as chlorine to shock a pool since it only makes problems worse unless you didn't have any CYA in the water to start with. The Leslie's "Green to Clean" is from Coral Seas and described here as a basic inexpensive algaecide (similar to a linear quat). Leslie's Power Powder Plus is Cal-Hypo. For every 10 ppm FC, it also increases Calcium Hardness (CH) by 7 ppm.

Yes, remove the 3" pucks as they are Trichlor and for every 10 ppm FC that they add they also increase CYA by 6 ppm. As for what to do, it will take a rather high chlorine level to kill the algae with the CYA at 150 ppm. A fast kill would take an extraordinary amount of chlorine, but you could do a slower kill at around 30 ppm FC using chlorinating liquid or bleach. You could use Cal-Hypo if your CH isn't too high already.

There are other alternatives for killing the algae, but they have side effects. For example, there are copper-based algaecides, but they can stain the pool and turn blond hair green if the copper level or the pH gets too high. There are sodium bromide products such as "No Mor Problems", but they turn the pool into a bromine pool, at least for a while (bromine does not bind to CYA so is not affected by it). There are products that add ammonia to the pool which combines with chlorine to form monochloramine that kills algae -- this might be your best bet other than chlorine alone since you can then clear the monochloramine with more chlorine, but I'm not familiar with a brand for this. Another alternative is a phosphate remover or various algaecides (including PolyQuat 60), but these are better at stopping or preventing algae growth and aren't good at clearing an existing algae bloom.

Read Defeating Algae .
hard8hopping
Pool Newbie
Pool Newbie
Posts: 2
Joined: Tue 09 Jun, 2009 02:22
My Pool: 15000 gallon, rectangular, in-ground, plaster
Location: Los Angeles, CA

How to kill algae despite 150+ PPM CYA?

Postby hard8hopping » Tue 09 Jun, 2009 03:29

Wow, that was a fast reply - thanks Chem Geek! :-) After posting, I went outside and emptied two gallons of liquid chlorine into the pool, i.e. all I had left. I thought it was better than doing nothing and wasting another nighttime opportunity to chlorinate. Given the purpose is to have the pool ready for my son's summer, I'd better not cause any other problems with side effects from other products.

I'll just bite the bullet and drain as that's the only real solution. Given it's a 15,000 gallon pool with 150ppm CYA, that's a lot of draining to get the CYA to its ideal level. Uh, what should the ideal level be? 40ppm? I completely drained the pool and refilled 4-5 years ago. I've since read that it's dangerous to completely drain. My pool was built around 1993. How should I drain? drain 1/3, test, repeat as needed? Thanks for your help!

BTW, I'm using AquaCheck test strips which measure pH, TA, FC, CYA. There's no calcium hardness which you mentioned. What other variables should I be measuring and what test kit would you recommend using?
chem geek
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How to kill algae despite 150+ PPM CYA?

Postby chem geek » Tue 09 Jun, 2009 10:31

You can do multiple partial drain/refill down to the level of the returns (with the pump off, obviously) or you can do continuous drain/refill but that uses somewhat more water. If you get the CYA down to 80 ppm, then that will be more manageable and OK, though you'll need to maintain a minimum FC of around 6 ppm. Whatever your CYA level, in a manually dosed pool maintain a minimum FC that is 7.5% of the CYA level unless you use a supplemental algaecide. Use of 50 ppm Borates can help as an insurance policy since it can somewhat inhibit algae growth.

You should get either the Taylor K-2006 kit you can get at a good online price here or the TF100 from tftestkits.net here with the latter kit having 36% more volume of reagents so is less expensive per test.

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