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Thread: cya (and salt) trouble

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    cya (and salt) trouble

    This month, I did about a 30% water drain from my pool. I figured that based on what I figure to be average and how far down I drained the pool. I let everything mix up a bit with the fresh water for several days and then I retested. My goal was to get the salt and cya back to what they should be. Since I didn't build the pool, I can't be certain of the volume. My experience over the past 4 years is that it is somewhere between 32-38000 gallons, based on the amount of chemicals, specifically acid, I have to add and also based on what I can measure in dimensions.

    Before the drain, my CH was fairly high (pushing 600) and my salt was a little on the high side as well.

    My salt and cya were, of course both very low. Salt was measured 3790 (my Zodiac Clearwater likes 4000 ppm, a little higher than other swg's) and my cya was 35, with a generous eye. It was probably closer to 25. I find this test to be very subjective. I even let the sample warm up to room temperature inside of my house for several hours before testing.

    So I tackled salt first, since the pool is still cold and the chlorine demand can't be that high yet. I had 2 50 pound bags of salt laying around and the pool calculator told me to add at least that. I added it and retested a few times over the week. The salt was not raising noticeably! I figured at this point that I was underestimating the volume.

    I then got some cya from my hardware store--Pace or HTH brand. I added 12 pounds, which was less than Pool Calculator's recommendations with conservative settings of 32000 and a starting cya of 35 (which I believed to actually be much lower since I could still see a shadow of a dot at 35).

    This weekend I replenished my salt strips. The salt measured much LOWER than before (3200), which I figured was more accurate because the old strips were expired. I had my husband add ANOTHER 200 lbs of salt, slightly less than Pool Calculator's recommendation.

    The next day (yesterday), I retested everything. I know it is less than a week since I added the cya, but I decided to measure that anyway.

    Here are the numbers I got:

    FC <.5
    CC <.5

    (I think the chlorine got used up because I started up my solar last week and there might have been some algae growing in there over the winter?)

    ph 7.5-7.6
    TA 160 (my fill water is 210, so it went up as expected with the drain and refill)
    CH 530 (not as low as I would have liked, but better than before)

    CYA 95-100!
    Salt 4780!!!

    What happened? How could the CYA and salt have risen like this? Should I wait a few more days and retest or tear apart the filter today and clean it thoroughly before any remaining CYA dissolves?

    The salt I am not that worried about because it is well within range for the swg. The CYA I'd really prefer to have at around 80. I certainly don't want it any higher than 100! I did not bring the water up to room temp as before, but I thought that would give me a LOW cya reading? I did buy new CYA reagent, but this reading was using the old stuff that I had used for the original tests.

    These things are now measuring as if my pool was a much lower volume than I know it to be as a minimum, not to mention the original 100 pound dosage of salt that barely made a dent in the salt reading....

    What is going on here? Any ideas?
    Salinda
    owner of ~37,000 gallon plaster IG pool/spa combo. Intelliflo VS+ filter pump, 2 hp whisperflo spa jet pump, Jandy Aqualink RS-6 with iAqualink upgrade, The Pool Cleaner 4x suction cleaner, Clean & Clear Plus 520 cartridge filter, Zodiac Clearwater LM2-40 SWG, Sta-rite 400k heater, solar heat pads and coils, Solar-Breeze NX.

  2. Back To Top    #2
    JasonLion's Avatar
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    There are quite a few things that could be going wrong and I suspect that more than one of them must be involved. However, it doesn't seem likely that any error in your guess about the pool size could be the issue. The pool would have to be 1/3 the size you think it is, which is implausible. Following are some of the things that help prevent mistakes when testing. If you failed to do any of these things it could have made a difference. The tests are usually fairly accurate even when the full procedures aren't followed, but now and again failing to follow the full directions can make a large difference.

    All water testing should be done with samples taken from 12 to 18 inches below the surface after the pump has been running for at least an hour. If you have a main drain it should be turned on to at least some extent to promote mixing of deep water with surface water. If you don't have a main drain, at least one return needs to be pointed down towards the bottom of the deep end to promote mixing. Failure to completely mix the water can sometimes have dramatic effects on salt tests.

    The CYA test should be done with warm water. If the pool is cold that means bringing the water inside to warm up before testing. It can also help to let the sample sit for more than the usual two minutes, say three or four minute. The CYA test can also be affected by any cloudiness in the water. If your water isn't crystal clear the CYA test will tend to read higher than actual.

    All testing vials/containers should be throughly rinsed first with tap water and then again with pool water before use.

    It also seems likely that at least one of the batches of salt test strips are bad.

    The only thing you can really do at this point is to do both of the tests again, taking care to follow the full procedures, and see if the results change at all.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  3. Back To Top    #3

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    Wow! I really appreciate the fast input.

    I'm thinking if maybe the salt wasn't all the way mixed yet, this would cause it to be slightly cloudy (I really didn't notice anything beyond a "little" dullness to the pool). Maybe this teeny little bit interfered with the cya test.

    I have a suction cleaner that is on all the time when my pump is on, so there is mixing from the bottom as well as the top. Unfortunately, I have one of those skimmers that ties the main drain into the skimmer with a float valve that has a trimmer plate on it. I usually leave it full open to the skimmer now since I have given the suction from the bottom of the pool over to the dedicated suction cleaner. I'm going to adjust the trimmer plate a little to allow some suction from the main drain, but I'm not sure how well that balancing works.

    What do you mean by letting the sample sit for the cya test for 2 minutes? My sample sat through all of my other testing and some other distractions before cya testing, so it was more like 20 minutes. Did you mean the pool water mixed with the cya reagent? I mix that and let that sit for 30 seconds before testing, as recommended.

    Since it hasn't been a full week, there still might be undissolved cya in the cartridges of the filter. Would you recommend cleaning them asap to prevent that from absorbing?
    Salinda
    owner of ~37,000 gallon plaster IG pool/spa combo. Intelliflo VS+ filter pump, 2 hp whisperflo spa jet pump, Jandy Aqualink RS-6 with iAqualink upgrade, The Pool Cleaner 4x suction cleaner, Clean & Clear Plus 520 cartridge filter, Zodiac Clearwater LM2-40 SWG, Sta-rite 400k heater, solar heat pads and coils, Solar-Breeze NX.

  4. Back To Top    #4
    JasonLion's Avatar
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    You are right, the usual CYA test directions are to mix the sample with the indicator and shake for 30 seconds. I forgot about that because I do it another way. Supposedly you can improve the accuracy by shaking for 30 seconds, let the sample sit for one or two minutes, shake for another 10 or 20 seconds and then take the reading. This is most important when the water is on the cold side, since it can take extra time for the indicator to react to create the cloudiness. This procedure is designed to prevent low readings caused by slow reactions with the indicator, which could have been an issue with your initial test.

    It might well be worth doing a regular backwash/cleaning of the filter.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  5. Back To Top    #5

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    Phew!!!!

    Retested today:
    FC 3.5 (I added 1 gallon of bleach yesterday to be safe and upped the swg output a little).
    CC <.5
    ph 7.6
    TA 170
    CH 530
    salt 4070
    CYA 65-70

    The salt was tested with the strip absolutely upright, and prior one was leaning at an angle. Would that make a difference? Maybe the previous sample was just too soon after the latest salt addition. I think the original test strips were suspect because they were out of date, but then again with the new test strip, the top line does not go completely dark--only about 50%, even after 10-15 minutes.

    For the cya test, I put the sample bottle into a warm water bath. The temp of the sample was 88° as measured with an instant-read thermometer. I got about 80 inside and 65-70 in bright sunlight outside. My plan now is to stop fiddling with cya until later in the season. I might try to get it to 80, but I think what I have now is adequate. I am not going to rinse the filters for a few weeks and the numbers might go up a little anyway.

    Based on this most recent test and my most recent salt addition, I can say with more confidence that the pool is around 35000 gallons since the salt level was around 3300 (between two lines) before adding 200 pounds of salt with these test strips. And yes the 3300 reading was with the strip straight up and down as for this latest reading.

    I'm going to tackle the TA now by reducing the ph to 7.2 for a little while. More fun!!
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    Salinda
    owner of ~37,000 gallon plaster IG pool/spa combo. Intelliflo VS+ filter pump, 2 hp whisperflo spa jet pump, Jandy Aqualink RS-6 with iAqualink upgrade, The Pool Cleaner 4x suction cleaner, Clean & Clear Plus 520 cartridge filter, Zodiac Clearwater LM2-40 SWG, Sta-rite 400k heater, solar heat pads and coils, Solar-Breeze NX.

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