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Thread: HUGE free chlorine loss

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    HUGE free chlorine loss

    Since openning my pool in early May, I have been experiencing huge FC losses daily. Water is crystal clear, however. My pool is 15K gallons, in-ground liner pool with cartidge filter. My numbers are good except for the FC loss. Ph- 7.4, CYA- 40-50, TA- 110. So I have held my pool at shock level or above for over 10 days now with no improvement. For example, last night at 8 pm I tested FC levels and they were at 18-19 ppm, which was a huge losss from the day before. So I added 8 gallons of 6% bleach and retested at about 11 PM. Fc was up to 42-43 ppm. This morning at 7 AM, FC was down to 37 or so, with no cc showing. At 10 AM this morning it was down around 28-29 ppm with cc .5<. I have been at this battle for too long, and it's getting expensive. My water looks crystal clear and inviting, but based on my testing, I am battling something. Oh yea, all my reagents were replaced with new ones because I thought they might be giving me bad results.

    Any suggestions would be greatly appreciated. I am thinking a partial drain and re-fill might be the least expensive option, since continued shocking has not worked.

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    dmanb2b's Avatar
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    Re: HUGE free chlorine loss

    Welcome to TFP.

    Your FC is way above shock level CYA of 50 = shock level of 20ppm. One would expect FC loss at levels that high during daylight of roughly 50%, so your loss is not drastic.
    Even dropping from 42ppm to 37ppm is not that drastic...the key to the overnight FC loss test is to test FC before sunrise. If there was any sun on the pool before 7am, that could be why you lost 5ppm. The higher your FC level, the more FC loss you will experience in terms of ppm, but the % lost should remain pretty consistent. Keep it at shock level until you pass the OFCLT.
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    Re: HUGE free chlorine loss

    How often are you testing and bringing your FC up to shock level?
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    Mr. Blue's Avatar
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    Re: HUGE free chlorine loss

    Is there a reason why you are trying to keep your FC so high?
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    Re: HUGE free chlorine loss

    I know that shock level for my pool with CYA of 50 should be 20 ppm, but that wasn't working. I guess I thought to bring it higher would be better for shocking purposes, but I guess that was flawed thinking. I just didn't want it to drop below 20 ppm when I wasn't around so I figured I was building in sort of a "buffer" for myself.

    I have been testing throughout the day today and it is steadily dropping. As of 3 pm it was at around 27 ppm but I did add 2 gallons of 12% pool store liquid chlorine to bring it back up earlier in the day. I also pulled the light out of it's niche and there seemed to be a lot of crud behind there. I scrubbed it and have left the light out of the niche to allow water to get in there and do it's thing.

    My question is why am I still doing all of this after about 11 days of being at shock level?? Has this ever happend before where it takes this long to eliminate a chlorine demand??

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    Mr. Blue's Avatar
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    Re: HUGE free chlorine loss

    If your CC has been 0 since the start, and your water is clear, what are you trying to accomplish?
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    Re: HUGE free chlorine loss

    Quote Originally Posted by Mr. Blue
    If your CC has been 0 since the start, and your water is clear, what are you trying to accomplish?

    I may not have been clear about CC in my testing. Most times it reads 0 but I have been getting sporadic readings of 0.5, but never more. The real issue is the huge daily chlorine losses. Normally my pool would lose 3-4 ppm on a hot summer day with lots of swimmers. This year, the water is still cold, and no one has been in the pool yet, but I am losing sometimes 6-8 ppm during the night. Seems like I am battling something and it will get expensive just adding large amounts of chlorine each day. I am wondering about a partial drain and re-fill if that might be more cost effective.

    Bottom line is the chlorine loss is WAY out of parameter for my pool.

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    Re: HUGE free chlorine loss

    I don't think a partial drain would help your situation. If you do have some organics hiding, doing a partial drain won't get rid of them.

    So, its sounds like if you were passing the OCLT, then everything would be OK. Can you describe in detail how you are performing the OCLT? At what time does the sun go down? When do you do your last bleach addition to the pool? How long do you wait before measuring the FC after doing your last bleach addition? Do you measure the FC in the morning before the sun comes up?

    If you are confident that you are properly performing the OCLT, then keep looking for algae (ladder, pool equipment, etc....).
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    Re: HUGE free chlorine loss

    Quote Originally Posted by faby3003
    I don't think a partial drain would help your situation. If you do have some organics hiding, doing a partial drain won't get rid of them.

    So, its sounds like if you were passing the OCLT, then everything would be OK. Can you describe in detail how you are performing the OCLT? At what time does the sun go down? When do you do your last bleach addition to the pool? How long do you wait before measuring the FC after doing your last bleach addition? Do you measure the FC in the morning before the sun comes up?

    If you are confident that you are properly performing the OCLT, then keep looking for algae (ladder, pool equipment, etc....).
    There was a day or two (not consecutive days) that my chlorine loss was less than 1.0 ppm from sun down to sunrise. When that happend I was going to keep at shock level for one more day as insurance. Trouble was that the next day I had losses of about 6 ppm overnite.

    Last night this is what I did...I tested at 8 pm ( sun was down and off pool) and chlorine was about 18.5 ppm. I added 8 gallons of 6% bleach at about 8:30 pm. I tested FC levels again at about 10:30 pm and they were 42-43 or so. No other chemicals were added. I got up at 6:30 am this morning and the sun was coming up but notshining on pool. I tested FC and it was 37 or so, and CC was 0 (don't have my log in front of me right now). I re-tested at 10 AM and now FC was at 28 or so, and CC was .5 . It was a sunny day so maybe some of that loss is due to UV, but I have never had losses like that. I have tested and re-tested my CYA just to make sure that that is not the cause of day time losses. 6 tests over 10 days show 40-50 CYA.

    I did remove the light from it's niche and there was a lot of crud back there. I scrubbed it and I am leaving the light out for the next 24 hrs so shocked pool water circulates in the niche. I pulled the ladder and removed the rubber feet that sit against the wall. I have them soaking in bleach. Not sure what else I can do?

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    Re: HUGE free chlorine loss

    That does sounds like a frustrating situation.

    If there aren't any other places that algae can be hiding, then I would look at the accuracy of your OCLT. Testing a FC of 40ppm could have a lot of variability - that's 80 drops of the R-0871 reagent!

    If it were me, I would leave my FC around 20 ppm at sunset, and measure FC using a 25mL sample instead of 10mL. Doing this, each drop counts as 0.2ppm instead of 0.5ppm. If you are testing at 10pm, I wouldn't add any chemicals after 6pm just to make sure everything gets mixed well. Then test in the morning using a 25mL sample again.
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    Smykowski's Avatar
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    Re: HUGE free chlorine loss

    That light niche thing will help. Are you still brushing the walls? That will also help with circulation.
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    JasonLion's Avatar
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    Re: HUGE free chlorine loss

    The amount of chlorine you lose during the day is a percentage of the amount you started with. When FC starts really high, like the 37 in the early morning you mentioned in the previous post, you will lose a lot of chlorine to sunlight very quickly just because the FC level is so high to begin with.

    The day time FC loss you mentioned several times is completely normal, and nothing to be concerned about. Day time chlorine loss should just be ignored as it really doesn't tell you anything.

    The overnight FC losses you have experienced are much more of an issue. You haven't said nearly as much about overnight loss, so there isn't very much to go on here. One thing that comes to mind is that doing the FAS-DPD chlorine test with FC levels as high as you are using is a little tricky. You might well be using too little R-0870 powder to start with, which could be throwing off the results. That is also a very large number of drops to count, with plenty of opportunity for mistakes.
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    Re: HUGE free chlorine loss

    Quote Originally Posted by JasonLion
    The amount of chlorine you lose during the day is a percentage of the amount you started with. When FC starts really high, like the 37 in the early morning you mentioned in the previous post, you will lose a lot of chlorine to sunlight very quickly just because the FC level is so high to begin with.

    The day time FC loss you mentioned several times is completely normal, and nothing to be concerned about. Day time chlorine loss should just be ignored as it really doesn't tell you anything.

    The overnight FC losses you have experienced are much more of an issue. You haven't said nearly as much about overnight loss, so there isn't very much to go on here. One thing that comes to mind is that doing the FAS-DPD chlorine test with FC levels as high as you are using is a little tricky. You might well be using too little R-0870 powder to start with, which could be throwing off the results. That is also a very large number of drops to count, with plenty of opportunity for mistakes.

    Hmmm...I didn't realize the FC loss as a percentage was such an issue. I will see what the loss is from sundown to sunrise tonight and get a feel for where I am at. My FC should be in low 20's tonight when I test. Thanks for your insight and help. I will let you know what happens.

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    linen's Avatar
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    Re: HUGE free chlorine loss

    Quote Originally Posted by JasonLion
    You might well be using too little R-0870 powder to start with, which could be throwing off the results. That is also a very large number of drops to count, with plenty of opportunity for mistakes.
    I think JL is on to something here. 8 gallons of 6% bleach should have raised your FC level to 51.5 ppm FC, not 43. I bet you need more powder at these high FC levels. How much have you been putting in? Also at high FC levels, you need to move through test fairly rapidly (like a drop every second or less) to get an accurate result.
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    Re: HUGE free chlorine loss

    I had the same problem last summer and it was the stuff behind the light the caused it. I had to shock my pool for about 2 weeks after cleaning out the light niche.
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    Re: HUGE free chlorine loss

    Quote Originally Posted by suep
    I had the same problem last summer and it was the stuff behind the light the caused it. I had to shock my pool for about 2 weeks after cleaning out the light niche.
    That's what I was hoping for....someone who has gone through this situation like me....hopefully the end is in sight!

  17. Back To Top    #17

    Re: HUGE free chlorine loss

    Quote Originally Posted by linen
    Quote Originally Posted by JasonLion
    You might well be using too little R-0870 powder to start with, which could be throwing off the results. That is also a very large number of drops to count, with plenty of opportunity for mistakes.
    I think JL is on to something here. 8 gallons of 6% bleach should have raised your FC level to 51.5 ppm FC, not 43. I bet you need more powder at these high FC levels. How much have you been putting in? Also at high FC levels, you need to move through test fairly rapidly (like a drop every second or less) to get an accurate result.
    As far as testing goes, when I am testing for FC levels over 30 ppm, I have been using 1 part pool water and 1 part distilled water. I mix those together and then do a 10 ml test. You end up using half of the titrating agent that you would normally use for such a high test. I realize there are testing errors involved in when using this strategy, but if I tested that way in the evening, I am testing that way in the morning. I think whether or not I use 80 drops in a full test or 40 drops in a diluted test, I think the real issue is I am showing large FC losses at nite which indicates I am battling something.

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