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Thread: High CYA - defeated algae, now to keep it that way...

  1. Back To Top    #1

    Join Date
    Sep 2015
    North Hollywood, California

    High CYA - defeated algae, now to keep it that way...

    Boy am I glad to have found this forum!

    I recently purchased a house with a pool and made the decision to DIY.

    Without knowing any better, I kept up the chlorine using tablets. Tested chorline/ph/alkalinity weekly, and didn't run into any problems for a solid 3 months. Over the weekend, I started seeing some algae. Went to the pool store, got some powdered shock and, per their advice, shocked multiple times. Tested chlorine levels throughout and could NOT understand why my problem was getting worse instead of better until frantic Googling led me here, where I learned about my arch-nemesis: CYA.

    After reading a few threads, it was obvious that my CYA levels were going to be off insane, thanks to my merciless use of powdered shock and chorine pucks. I ordered a proper test kit (Taylor K2006) and ran out to get as much liquid chorine as I could fit into a shopping cart. While waiting for the test kit to arrive, I started dumping liquid chorine into the pool, brushing like crazy, and cleaning my ancient filter twice a day. Lo and behind, the water was clearer than I've ever seen it before the kit even arrived at my door 2 days later. (BIG thank you to everyone on this forum for this!)

    Algae's been gone for the last 2 days. Here are today's test results (assuming I did things right):
    FC 10.4
    CC 0 (Hooray, this is a good sign, right?)
    PH 7.8 (I will knock this down a few notches this afternoon)
    ALK 110
    CH 300
    CYA 120 (1st test was off the chart, so I did the half pool water, half tap water, results x2 trick to get 120)

    I live in southern California and draining/refilling isn't really an attractive option right now, not only for the expense, but I'd also prefer not to be drought-shamed by my brand new neighbors (forgive my sarcasm - I'm sure they're all very nice people). So, I'll be taking the hard route and learning how to manage my pool's CYA until I can scrape together enough to try a reverse osmosis treatment which I see some on the forum have reported success with. In the meantime, I'll keep the cover off, be more aggressive with cannonballs and splashing around to displace water more frequently, and will spend all the rest of my time/energy willing it to rain.

    So - good people at TFP, my next question is: what other problems do I need to keep an eye out for with a CYA as high as mine? I plan to keep my FC between 10-12 at all times (which looks ok according to the Chlorine/CYA chart) - higher if I know we won't be jumping into the water for a few days. It's my understanding that chlorine levels in that range wouldn't be unsafe for swimmers because of the CYA - or am I unknowingly putting people at risk despite the crystal clear, irresistibly inviting algae-free water?

    Any other tips to share? Also - I can't say enough - thank you to everyone at this forum for sharing your knowledge. I feel like I've saved so much time/money already, and wish I'd have found the site before I entered the dark puck-era months of my pool ownership life.
    total pool ownership n00b newly endowed with a 23,000gal in-ground 15'x32' gunite pool, the oldest DE filter every pool person i spoke with has ever seen, and a neat little scrubby brush.

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    bmoreswim's Avatar
    Join Date
    Jul 2012
    Central MD

    Re: High CYA - defeated algae, now to keep it that way...

    You can swim with FC up to shock level. Since your CYA is so high, your shock level is stratospheric. Most of your chlorine is buffered or bound by the CYA and therefore harmless.

    You absolutely don't want to have an algae a outbreak with CYA that high because it takes a tremendous amount of bleach to maintain FC at shock level to perform a SLAM.

    So just be fastidious about your testing.
    18'x38' Rectangle (3'-8 1/2' deep w/ diving board) - 27K gal. w/ gray plaster
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  3. Back To Top    #3
    Agent99's Avatar
    Join Date
    Aug 2008
    San Jose, CA

    Re: High CYA - defeated algae, now to keep it that way... Now I'm all distracted! Welcome to TFP!

    I suggest you 'quietly' water your lawn/plants with your water over the 'winter' and then with all the rain we'll certainly get, you'll have cut that CYA in half by Spring!!!

    Your overly high FC for your CYA level is okay since most that will be locked up by the CYA so it is perfectly safe to swim in.

    You may wish to continue your SLAM now that you can properly test but at 120, it'll take a small truckload of bleach to accomplish it. Your SLAM level looks to be 43. FC level should be like 14ish.

    There are 3 criteria to pass SLAM and to ensure algae is totally gone:
    (1) Clear water
    (2) CC <= 0.5
    (3) OCLT falls 1 or less
    25k IG/Spa Figure 8, 18x36, Pebble Sheen Blue Granite, Sta-Rite S8M150 Cartridge Filter, Pentair 460805 400k BTU Heater & 011018 IntelliFlo VarSpd
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  4. Back To Top    #4

    Join Date
    Aug 2015
    McKinney, TX

    Re: High CYA - defeated algae, now to keep it that way...

    For what it's worth concerning high CYA levels ---

    I just bought a house with our first pool (4 weeks ago), and also had CYA levels in excess of 120. Water bills in my area are astronomical ($500-600 in summer), so I really didn't feel like draining a third or even half of the pool and replacing water. However, I did put a hose in it a few times to at least dilute the water a bit. I was able to get the CYA down to about 100 in this manner. Then I made sure that all other levels were ABSOLUTELY perfect, and I used two bags of the Bio-Active chemical reducer. It worked like a charm. (It can't reduce super-high CYA levels, and I'm sure that half of the people who try and use it haven't prepared their water properly ... but it worked fine for us.)

    I'm still a newbie, but I must say that this site has been a treasure trove of great info ... so appreciative that my wife found it !

    Bruce & Sarah
    37.5k pebble sheen pool, CCP420 cartridge filter system, No SWG

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