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Thread: Massive chlorine demand and green tint, but no metals

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    dwagner's Avatar
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    Massive chlorine demand and green tint, but no metals

    I have what I feel like is an unusual situation with my outdoor pool, and I'm hoping you folks can help shed some light on it.

    Our pool is an outdoor in-ground 14kgal pool. I don't have any railings or ladders or other metal in it (except for a single pool light) and it's got a painted plaster surface. It sits with its surface exposed in the Texas sun most of the time (I don't have any covers or anything). My filter is DE and when everything's running well I backwash about monthly. We moved into this house about 1.5 years ago and it's our first pool, so we still have a lot to learn.

    Earlier this year I noticed our FC falling to zero overnight from about 3-4 ppm. At the time I was not measuring CC. I did a little research, asked around, and determined that since my CYA was over 100 it was chlorine lock and that I needed to partially drain and refill the pool. After the third time that happened I had decided that chlorine lock wasn't a real thing and just kept on doing what I normally did at that time: add more tablets and dichlor (I know better now). My CYA got upwards of about 250 ppm and I got sick of it and just let the pool sit; I decided to see if the CYA would decay on its own. As an aside, we absolutely hate draining the pool because we have to babysit the entire process because our pool is on a tiny hill about 1-2 feet higher than our neighbors' yards. Any time we drain any significant amount of water we flood our neighbors, making draining the pool a huge pain. Needless to say I shortly had a very fancy expensive dark green swamp in my back yard.

    Maybe a month or two later I measured the CYA and it had dropped to about 50 ppm. A few days later the CYA appeared to be very low, maybe 10 or 20. Something was creating CYA demand. I didn't think too much about it, feeling that my troubles were nearly over and that I was so smart to have just let the problem take care of itself. By that time I had learned that in the hot Texas sun dichlor is pretty much always a bad idea and that I could use straight bleach to create the necessary FC to sanitize the pool as long as the CYA was reasonable. I resolved to continue using trichlor tabs to keep the CYA in range and to use bleach or calcium hypochlorite to shock and raise the FC when necessary, keeping a close eye on hardness to make sure it didn't get out of control (it has always sat right around 250 ppm and never given me much trouble throughout all of this).

    It was at that time that I realized that no matter how much chlorine I put in the pool I never had any FC after about an hour or so. I used up my remaining dichlor and tabs to raise the CYA to about 50. Whether I used bleach, cal-hypo, or dichlor, and whether I added it in the evening or during the day, I never could keep any significant (> 1 ppm) FC more than about an hour. I did manage to clear up my algae with Ram Mustard Out 60 which should not create any additional chlorine demand. Every few days I'd vacuum up any dead algae with our filter set to waste in an effort to clean the pool as quickly as possible and to get rid of whatever problem the pool might have by replacing the water bit by bit.

    If you're still with me, that brings my story up to the beginning of this week. There was still zero chlorine, even with at least 2 tabs in the pool at all times, the pH around 7.4, and the CYA at around 50-60. I'm still testing with strips, but I'll probably get a decent test kit this evening. My girlfriend did a little research on her own and found out that it might be ammonia in the water from bacteria that had metabolised the CYA. Excited, we ran out and bought an aquarium ammonia test kit, and tested the water right there in the car. Sure enough, we were showing about 0.4 ppm of ammonia based on that kit. We were thrilled! From the calculations we'd made based on a few other posts on this forum, we ran in and bought about 4 gallons of 8.75% bleach, thinking that ammonia had been our problem all along and that we could put that bleach in and finally have a healthy pool again. Since then we've been dumping huge amounts of chlorine into the pool and we can't get the ammonia test to show less than about 0.25 ppm.

    This afternoon the CYA looked close to zero and I added 2 pounds of cal-hypo and about 48 oz by volume of dichlor. I measured 5 minutes later and my strips showed > 10 ppm FC. Around 25 minutes later my strips indicated < 1 ppm FC. I had also started noticing a green tint to the water when I shocked it that would last about 15-20 minutes. Note that the water appeared perfectly clear to me; it was just a little green instead of blue. I've never had any problem with metal in the water and I haven't used any copper-based algaecide in over a year. Just to make sure, I took the test in to a local pool store who of course forgot to run the metal tests before they dumped the water out. They did find 4 ppm FC and 0 ppm CC with 100 ppm CYA. The pH is a little low (6.8), which I'll fix as soon as I get home this evening. So I have the following questions:

    1) Why is my pool still not holding chlorine, and how do I get it sanitized? (Obviously this is the most important thing)
    2) Where is my CYA going? Should I start off trusting my strips or the pool store until I get my own more reliable test kit?
    3) Why is my pH low when I've been adding a ton of cal-hypo, which ought to be raising the pH?
    4) What in the world is that green tinge when I shock?

    Help!
    12'x24'x52" AG pool. Hayward S210T Sand Filter, Hayward 15922s 1hp dual speed pump

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    dwagner's Avatar
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    Re: Massive chlorine demand and green tint, but no metals

    Just added soda ash (according to the poolcalculator.com) to bring up the pH and while it's circulating I thought I'd post my other stats from the pool stores:

    FC: 4 (strips: 0)
    TC: 4 (strips: 0)
    CC: 0 (strips: N/A)
    pH: 6.8 (strips: ~7.3, but I've already added the soda ash)
    CH: 130 (~250)
    Alkalinity: 85 (80)
    CYA: 100 (strips say ~70)
    TDS: 850 (strips: N/A)

    Honestly most of these numbers are inconsistent with what I've been seeing from my test strips, so I really don't know what to trust. I made a friend at the pool store who seemed pretty interested in getting to the bottom of this and I'm going to take him more samples which he'll test for nitrates along with the metals.

    I'm also trying to brush at least daily, and I've just now checked my jets to make sure they're pointed towards the bottom of the pool to maximize circulation.
    Also I tend to slowly pour all of my chemicals into the single skimmer on the pool, is that reasonable?
    12'x24'x52" AG pool. Hayward S210T Sand Filter, Hayward 15922s 1hp dual speed pump

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    Re: Massive chlorine demand and green tint, but no metals

    Dwagner, welcome to the forum!


    Wow! Sounds like you have been having some fun.
    I don't have a lot of time to go into all of your problems, but here's the basics of what you need to do.
    1. You ultimately have no idea what is going on with your pool because you are using test strips.
    You might as well throw a dart at a dartboard marked with pool chemicals and levels. Because that's about how accurate they are. Right along with the pool store's results.
    2. You need a proper test kit, you won't find one locally. See the link in my signature. They ship fast and their customer support is bar none the best.
    You can't shock your pool without a proper and highly accurate test kit, it just can't be done.
    Read the link in my signature on shocking your pool and follow all links inside that article, reading those as well.
    3. Read Pool School, link in my sig, or upper right button @ top of pg. Then re-read it some more.
    4. I'm certain you have copper in your pool, as it's oxidized by chlorine. Based on your description of it turning green when you add chlorine, especially. Once you add anything at all with copper, it stays there.
    5. Don't trust that pool guy at the store, he's not your friend. At least not business/pool wise. He's just there to bleed your wallet dry and tell you lies, perpetuated by the industry that he believes to be true and correct.
    6. Stop adding CYA/CalHypo/Dichlor/Trichlor/Pucks to your pool. Only use bleach or liquid sodium-hypochlorite. Not Lithium-Hypo, it's a RIP!

    You can't do anything really until you get a proper test kit. So go order that ASAP!!!!
    You'll probably get it in a couple days, tops if you do pri. mail.
    Thanks for reading... - Tony
    Da' Pool: Intex 15'x42" 3284gal AGP EasySet (Inflatable Ring) - (Summer 2014: 27' round EW /w 6.5' deep end @ 22,500gal)
    Pump & Cart Mod: 1000gph Cart. 5ft² - 2 nylons, 24/7 OP. Traps bugs/bits, lasts longer/cleans easier = Happier Pool Owner!!
    The Bible for a "Trouble Free Pool" life = PoolSchool, the BBB method a TF100 test kit(Recommend Kits Compared). - Cleaning a Sand Filter
    Water looks like GLASS, if yours doesn't...SLAM IT! Feels nice and never been happier!!! :D

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    Re: Massive chlorine demand and green tint, but no metals

    If you can find threads about a similar problem (there are some, somewhere!) read as many as you can while you wait for your test kit. This might give you a good idea what to expect, along with the advice in pool school. The test strips are notoriously bad at giving accurate results.
    26' X 52" Intex Ultra Frame. Intex Sand Filter
    26' X 52 Intex Ultra Frame Install
    You can lead a horse to (clear) water, but you can't force him to swim in it!

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    Re: Massive chlorine demand and green tint, but no metals

    Welcome to TFP!

    I describe what happened to me in my pool when I had a bacterial conversion of CYA to ammonia in thread It Can Happen to Anyone - Zero Chlorine, CYA --> Ammonia. This post in that thread is a summary log of what happened and how I handled it. If you had a lot of CYA degraded, then it will take extraordinary chlorine levels since it takes 2.5 ppm FC for every 1 ppm CYA that is degraded to ammonia. The only thing going for you in your favor is that your ammonia reading is low so maybe the bacteria converted some of the CYA to nitrogen gas instead (technical details in this thread).

    The easiest way to find out the true chlorine demand for your pool, assuming your CYA is now zero so that the bacteria having nothing more to convert, is to do a bucket test where you take a bucket of pool water and add 6% bleach to it to see how much it will take before the FC holds. 1/4 teaspoon of 6% bleach in 2 gallons is 10 ppm FC. Unfortunately, it may be better for you to yet again to a partial drain/refill of your pool.

    For future reference, do not think that Trichlor won't increase your CYA level. Though Dichlor increases it faster, both increase it. And Cal-Hypo increases CH. The following are facts that are independent of concentration of product or of pool size:

    For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
    For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
    For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    dwagner's Avatar
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    Re: Massive chlorine demand and green tint, but no metals

    Thanks for the responses! I'll try to order a kit tomorrow morning.

    ChemGeek, I've been voraciously reading what posts I can find that fit what I've been seeing, especially that first post you linked. That's actually the post that convinced us that we might have ammonia problems. I think you may be right about completing the conversion all the way to nitrogen gas; it certainly had enough time and the environment to establish an entire fauna.

    I will certainly try the bucket test once I have a chlorine test that I trust. That's a great idea.

    I only added the dichlor and trichlor because I believed the CYA was low. I shouldn't have trusted the value on the strips or at least should have waited to see if the measurement repeated for more than a few days. I currently don't have any tabs still in the pool and don't plan on adding anything with CYA in it for quite a long time.

    So I talked to the guy at the pool store tonight after taking him fresh water samples. He was as baffled as I am. He also didn't try to sell me a single thing apart from a better test kit after I mentioned being in the market for one (an OTO tester, but since I want the increased range of FAS-DPD I turned him down). He seemed genuinely curious as to what's going on in the pool. Unfortunately he didn't have the nitrate tests there, but promised he would have them by Monday and run another test for me. Here are a few of our observations:

    1) There was zero iron or copper content in the pool. Same for phosphates, borates, bromide, and just about everything else he tested for.
    2) After putting 5 gallons of 8.25% bleach into the pool this evening, it has remained fairly green for about two hours so far.
    3) The jets are also showing small bubbles now, which they weren't before. The bubbles don't seem to last and don't cause any kind of foamy buildup on the surface.
    4) He tried 4 types of strips that they had there in the store; all showed 0 FC. OTO showed about 1 ppm, and DPD showed about 0.6-0.8 ppm.
    5) My calcium levels are actually slightly low (~140) so I'll continue to use the cal-hypo when I don't have bleach on hand.

    ChemGeek, did you ever notice a green tinge to your water when you were oxidizing ammonia? I appear to have an ammonia test kit very similar to yours; did you ever get it to come out fully yellow, or is "zero" not quite as yellow as the card indicates?
    12'x24'x52" AG pool. Hayward S210T Sand Filter, Hayward 15922s 1hp dual speed pump

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    Re: Massive chlorine demand and green tint, but no metals

    In my case, I caught the conversion fairly early after only a few days so the water only got dull/cloudy and didn't turn green either from algae or from metals. The ammonia kit did get to zero, but it's an approximate test and I think the chlorine demand bucket test is the most reliable way for you to know how much chlorine you will need. The main decision will be whether to do a partial or large drain/refill or whether you just blast it with lots of chlorinating liquid or bleach.

    If the OTO and other chlorine tests aren't showing zero, then it's possible you might be near the end and able to soon hold chlorine. Just note that when I got past the "fast" chlorine usage point where it oxidizes ammonia, I still had days of high but not extreme chlorine demand which I attributed to oxidizing partially oxidized CYA.

    I wouldn't worry about the green tinge until you are able to get your chlorine situation under control. Otherwise, you'll just be fighting bacteria in the pool. If you lower the pH and the green lightens up, then it's most likely metals (perhaps from copper in the Trichlor pucks/tabs you were using -- do you know the brand/name of the product?).
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Re: Massive chlorine demand and green tint, but no metals

    Just a side note, do not add your chems to the skimmer. Add them over the returns in the pool, you don't want the concentrated chems flowing through your equipment.
    16k gal plaster with raised spa, Jandy DEV60 filter, 2 HP 2-speed SHPF Jandy Stealth pump
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    Test Kits . Pool Math . Chlorine/CYA Chart . The SLAM Process

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    Re: Massive chlorine demand and green tint, but no metals

    i think the overriding message that needs to be conveyed to you is that your need to get your own decent test kit. Once you get the TF100, then and only then can you truly start to get on top of your problems.

    Using the Pool Store and Strips for testing is only going to cause you confusion and inaccurate readings, see this thread for a comparison of strips v other devices for a little clarity the-differences-in-pool-testing-equipment-t53470.html

    It will hopefully drive home the message regarding how accurate your strips really are. Listen to Chem Geeks advice regarding counteracting the chlorine demand, and you will get over it.

    Calcium Hypochlorite is fine to use, but I would be wary about your CH levels until such time as you have a accurate and comprehensive result of your pools water chemistry, your results at the moment can only be taken as bona fide.

    Regards
    Stuart
    Stuart Murray
    Scotland UK
    UK NPPOC

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    dwagner's Avatar
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    Re: Massive chlorine demand and green tint, but no metals

    Thanks for the advice everybody. I won't be trusting the strips any more. I bought a DTD test to at least be able to measure FC until the full test kit comes in.

    By the way, I'm pretty sure the green tint is from the bleach itself. Previously I was pouring it straight into the skimmer at night, but today I poured it directly into the pool above one of the returns (thanks ping) and to my surprise it was greenish even before it hit the pool! I guess that's what I get for not doing my whites on my own.
    12'x24'x52" AG pool. Hayward S210T Sand Filter, Hayward 15922s 1hp dual speed pump

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    Re: Massive chlorine demand and green tint, but no metals

    Concentrated bleach has a yellow-green color, but this will NOT result in any green tint in the pool itself since it is so diluted. The green you are seeing in the pool is probably metals -- either copper or if you have a blue vinyl liner then it could be iron since yellow over blue looks green. The green could also be algae if the water is a cloudy green (if clear green, then it's more likely to be metals).
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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