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Thread: Phosphate Frustration, Low FC

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    Phosphate Frustration, Low FC

    We have a 24' AG pool that was installed one year ago. I am new to owning pools, but have a strong background in science - which makes it all the more frustrating that I cannot seem to get our pool levels to stay consistently where they are supposed to be.

    Last summer I had a terrible time keeping the chlorine levels above 1. We had an in-line chlorinator running on maximum, I added 4 cups of 12.5% liquid bleach per week, algeacide, stain-guard - everything the pool store said to do. We had two algal blooms resulting in lost swimming time and grey hair.

    We opened the pool 3 weeks ago to cloudy water with leaves on the bottom. I added 5 gal 12.5% liquid chlorine, metal magic (since we had an iron issue last summer and we needed to add water), 2 gal liquid shock, 1 packet powdered shock, and algeacide over a couple weeks time and the water is now clear. Pool sits partially under a large black maple tree and gets quite a bit of debris which we remove daily.

    I took a water sample to the local pool place 2 weeks ago and they said my phosphates were really high - well over 1000. I bought my own test and verified that. She recommended PhosFree. I did extensive reading on phosphates in pools on your forums and elsewhere which has left me frustrated and confused. I tried the PhosFree - adding a total of one 3L bottle over a few days time - and the levels did not seem to drop at all. We had to add water from all of the backwashing and vacuuming and our well water (we are in the middle of farmland and have farmers spraying all of the time) tests at 500ppb phosphates right out of the tap. I am wondering if the metal magic added the rest?

    Here is the problem as I see it - it seems to me if I continue to add PhosFree and backwash and add more water, I am never going to get ahead of it. I realize that many people think phosphate levels are irrelevant - to a point. I am not sure exactly how high mine are - just know they are over 1000ppb. My CYA levels started at 0. I have added 2 pounds stabilizer to the skimmer which, after a week, raised it to 10. I put another pound of stabilizer in a sock and it is dissolving now.

    QUESTION - Is it possible that super high phosphate levels are making it more difficult for me to keep my FC where it needs to be - or should I completely ignore it? If I ignore phosphate, how much chlorine should I have to be adding and how often in addition to the five 3 inch pucks I have floating in a dispenser? Why do I continue to have such low FC levels? (I did the SLAM method and got my CCs <0.5ppm and yes, I do have a kit I use to figure out my own FC/CC numbers). Am I destined to have to add extra Cl if I don't lower my PO4??

    pH = 7.3
    FC 1.5 (have been adding a couple of cups CL every night)
    CC <0.5
    CYA about 10 last time tested at pool store
    PO4 >1000 in pool, well water from tap = 500ppb
    Pool is currently clear

    Thank you for your help!!!!!!!!!!!!
    kelly
    kelly
    24' AG Round, 14,500 gal, 1 year old
    1.5 HP Pentair Pump, Sand Filter

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    JasonLion's Avatar
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    Re: Phosphate Frustration, Low FC

    Quote Originally Posted by bioteacher View Post
    QUESTION - Is it possible that super high phosphate levels are making it more difficult for me to keep my FC where it needs to be - or should I completely ignore it?
    No, it is not possible. My phosphate level is a couple of thousand and I don't have any problems from that. Just ignore phosphates.

    Your problem is that CYA is too low, so you are losing all of your chlorine to sunlight.
    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

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    Re: Phosphate Frustration, Low FC

    I have added a total of 3 pounds of stabilizer in the past three weeks - the sock with the last pound I added 5 days ago looks empty. I tried testing CYA last night, and it registered less than 30 (my test won't read anything less than 30). Should I wait a few more days and re-test CYA, or add more? How much more?

    Thanks!
    kelly
    kelly
    24' AG Round, 14,500 gal, 1 year old
    1.5 HP Pentair Pump, Sand Filter

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    Mod Squad JVTrain's Avatar
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    Re: Phosphate Frustration, Low FC

    3 lbs should get you in the range you want to be in if your pool volume is correct. When was the last time you added CYA or more precisely, when was the last time it was all dissolved?
    Joel - TFP Moderator - Minnesota - **Become a TFP Supporter!** Helpful Links: ABCs of Pool Water Chemistry - SLAM Procedure - Chlorine/CYA Chart
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    Richard320's Avatar
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    Re: Phosphate Frustration, Low FC

    3 lbs of stabilizer in a pool your size adds 25 CYA. If you've been backwashing, you've lost some of that. So it is not surprising you show a low CYA reading all the time. Just add more. Maybe 2.5 - 3 lbs. Plug your numbers into poolmath. Also, if you go down to the bottom where it says Effects of Adding Chemicals, you can see what each chemical will do.

    What test kit do you have? You should try an overnight loss test, but without the right test kit, you can't. If it passes, then the problem is not algae, and you can happily just boost CYA and FC levels and move along.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
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    Mod Squad jblizzle's Avatar
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    Re: Phosphate Frustration, Low FC

    Did you use PoolMath to determine how much stabilizer to add?

    3 pounds in your pool will only add 25ppm of CYA ... and it takes up to a week to show up on the test. So, I am not really surprised it still shows less than 30ppm (you may have started at 0).

    I would add another 1-2 pounds.
    Jason, TFP Moderator
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    Re: Phosphate Frustration, Low FC

    The last of the three pounds just dissolved yesterday. Yes, I have had to backwash a few times after vacuuming and when the pressure went up after adding the PhosFree, so I am sure some CYA was lost there. I have a Taylor Test Kit K-2006. I will try the overnight loss test tonight and I will add more stabilizer. There is quite a bit of pollen/dirt? in the bottom that I have to keep vacuuming up - is it ok to backwash after each vacuum?

    Thanks!!

    kelly
    kelly
    24' AG Round, 14,500 gal, 1 year old
    1.5 HP Pentair Pump, Sand Filter

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    JasonLion's Avatar
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    Re: Phosphate Frustration, Low FC

    It is fine to backwash after vacuuming as long as you don't have any CYA in the filter dissolving.

    We recommend adding CYA in a sock in the skimmer, that way it isn't sitting in the filter when you backwash.
    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

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