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Thread: Cant get the FC to hold

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    Angry Cant get the FC to hold

    I was called this morning by a friend and who Im now trying to help, he is in Spain and staying in a rented house for the summer. He knows a bit about pools as do I but neither of us are experts. The pool condition is less than perfect as chlorine tabs have been used for years and little water has been replaced so we can assume that the CYA is off the scale and there is no possibility of re-filling the pool because there are water shortages in the area!!!

    Background; a week ago the pool was green, since that time the pool has been shocked with granular shock (but probably only to 10ppm!) several times and although the water had cleared it was not crystal clear and the chlorine would not hold. This is a 42000 litre pool.

    Last night at 20:30 the pool was shocked with 2kg 91% trichlor, I think this should have given 45ppm.

    08:30 it was back to 2ppm.

    08:30 shocked again to 22ppm

    12:30 it was back down to 6ppm

    13:30 down to 5.2. At this point though the water was crystal clear.

    17:00 down to 2.7ppm.

    17:30 shocked with 20kg of 15% bleach (am I right in assuming this is about 18 litres?) I believe will have raised the FC by 65ppm.

    The test kit available is not able to test above 13ppm so have suggested diluting the pool water by 10 parts and X10 the resulting reading, is this sound advice?

    18:30 the reading is 72ppm

    19:30 the reading is 52ppm

    Other than adding another 20kg of bleach Im not really sure what to do, any ideas?

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    Mod Squad jblizzle's Avatar
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    Re: Cant get the FC to hold

    Only took you 5 years to post

    You guys could be damaging that pool!!!
    You MUST know the CYA level to know the proper FC level to use to follow the ShockLevelAndMAINTAIN Process.
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    Re: Cant get the FC to hold

    Quote Originally Posted by jblizzle View Post
    Only took you 5 years to post

    You guys could be damaging that pool!!!
    You MUST know the CYA level to know the proper FC level to use to follow the ShockLevelAndMAINTAIN Process.
    I understand the point you are making but we are where we are. As you will know its very difficult to measure CYA above 100ppm even with good equipment, which is not available at the moment, but based on my own experience of using tabs in a pool for 4 years with minimal replacement of water I would expect the CYA to be around 400ppm. I should say that this was before I was educated by this and other forums and converted my pool to liquid chlorine. Assuming that the CYA is 400ppm, and I very much doubt that it is less than this, the recommended shock level is 75ppm so I dont think we are in danger of damaging anything, indeed it could be that we are not raising the FC sufficiently to adequately kill the remaining algae.

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    Simple question!

    You may have seen in another post that I am struggling with a pool that has VERY high CYA.

    I know that I can dilute pool water by 10 to 1 to test for CYA, incidentally I then get a reading of 30/50 which confirms my view that the CYA is impractically high! However, does it also follow that I can dilute by 10 to 1 to test for high chlorine?

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    Re: Simple question!

    No, it would not be accurate to do that. What are you using to test FC?
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    Re: Simple question!

    As mentioned, the more you dilute the less accurate the test is.

    Please keep all your questions in one thread.

    Cant get the FC to hold

    Dom
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    Re: Cant get the FC to hold

    I would think it'd be a good idea to do a drain and refill to lower the CYA.
    26' X 52" Intex Ultra Frame. Intex Sand Filter
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    Re: Cant get the FC to hold

    Quote Originally Posted by PAGirl View Post
    I would think it'd be a good idea to do a drain and refill to lower the CYA.
    Agreed but as I said above this is not an option as there is a water shortage in the area

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    Re: Simple question!

    Quote Originally Posted by PAGirl View Post
    No, it would not be accurate to do that. What are you using to test FC?
    Not a FAS/DPD sadly so the readings are inaccurate at best anyway.

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    Re: Cant get the FC to hold

    Quote Originally Posted by macgd016 View Post
    I understand the point you are making but we are where we are. As you will know its very difficult to measure CYA above 100ppm even with good equipment, which is not available at the moment, but based on my own experience of using tabs in a pool for 4 years with minimal replacement of water I would expect the CYA to be around 400ppm. I should say that this was before I was educated by this and other forums and converted my pool to liquid chlorine. Assuming that the CYA is 400ppm, and I very much doubt that it is less than this, the recommended shock level is 75ppm so I dont think we are in danger of damaging anything, indeed it could be that we are not raising the FC sufficiently to adequately kill the remaining algae.
    Where did you get that "recommended shock level of 75ppm"?

    Shock level is 40% of CYA (400 X 0.4 = 160)
    Minimum FC is 7% of CYA (400 X 0.07= 28)
    Maintanence FC target is 13% of CYA (400 X 0.13 = 52)

    If the CYA is really 400ppm the pool is unmanageable. I know that is not what you wanted to hear, sorry.

    You need to stop guessing and get accurate measurements. Right now, best case scenario is that you are just wasting money, worst case is that you are damaging the pool.

    Dom

    EDIT:
    Please keep all questions in one thread.

    Simple question!
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    Re: Cant get the FC to hold

    Quote Originally Posted by domct203 View Post
    Where did you get that "recommended shock level of 75ppm"?

    Shock level is 40% of CYA (400 X 0.4 = 160)
    Minimum FC is 7% of CYA (400 X 0.07= 28)
    Maintanence FC target is 13% of CYA (400 X 0.13 = 52)

    If the CYA is really 400ppm the pool is unmanageable. I know that is not what you wanted to hear, sorry.

    You need to stop guessing and get accurate measurements. Right now, best case scenario is that you are just wasting money, worst case is that you are damaging the pool.

    Dom

    EDIT:
    Please keep all questions in one thread.

    Simple question!
    The 75ppm figure came from the Poolcalculator.com, I've used this for years but see it has been superseded by Poolmath, my mistake, I should done the calculation given me by Richard some time ago rather than being lazy!

    I agree that CYA at 400ppm is unmanageable so I don't mind you saying so but its not my pool and as I said at the top nothing can be done about it due to water shortages.

    I am also frustrated that accurate readings cannot be taken so there is no need to shout and there is little chance of damage to the pool because it is tiled and all of the filtration system components are plastic.

    To be clear, if it was my pool I would drain and refill it but its not my pool and these things cannot be done.

    So as said before we are where we are and if anyone has any practical suggestions on how we might move forward I would welcome them.

    My current thinking is to let the FC drop back to a readable level, use liquid chlorine and put 3ppm in per day and see what happens. If the FC goes up reduce the daily does of chlorine and if it drops like a stone think again!!

    Two questions I do have though are:

    1. Some of the chlorine is bound by the CYA, if for instance the FC reading is 10ppm but the CYA level is such that half of the FC is 'bound' by the CYA what would the FC reading be expected to be if 1ppm of FC is used to kill algae. Would you be left with a reading of 9ppm or 8ppm.

    2. I have read somewhere that sunlight degrades FC as a %, if this is the case where 1ppm might be lost from a pool with 3ppm 10ppm would be lost if the pool started at 30ppm, is this the case?

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    Re: Cant get the FC to hold

    If I was shouting I would use all capital letters....... I made that statement bold to signify it's importance.

    What do you expect 3ppm of FC to do for a pool with a suspected CYA of 400ppm?

    The FC test will measure all FC in the pool, including any bound to CYA. Any that has been oxidized (killing algae) will not register as it is no longer FC.

    CYA will buffer FC loss, how much depends on the CYA level, which you are guessing at this point.

    Good luck with this pool. My honest opinion is that it will be much more cost effective to replace water if it is available to be trucked in, or a Reverse Osmosis treatment to lower the CYA.

    Dom
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    Mod Squad tim5055's Avatar
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    Re: Cant get the FC to hold

    I'm really confused as to what "answer" you are looking for. Our entire system is based on accurate testing and basing actions on that testing. We do not base answers on "guesses".
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    Mod Squad kimkats's Avatar
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    Re: Cant get the FC to hold

    Dom has you well covered in what should be done.

    It would be irresponsible for us to say anything other than what has already been said.

    Good luck with the pool.

    Kim
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    Re: Cant get the FC to hold

    If they can't refill due to a water shortage is a reverse osmosis service an option to get the CYA down?
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    Cant get the FC to hold

    Without accurate test results, it's hard to give good advice. But here's a possibility -

    If your friend can clear the pool then try to use liquid chlorine to keep the FC above 15ppm and the pH within normal ranges. Between 15-20ppm, your active chlorine level will be high enough to kill bacteria and viruses by too low for algae control. You will need to use a secondary sanitizer/algaecide to keep the algae under control. If your friend has access to Polyquat-60, that would be a good place to start. It will require regular weekly dosing in order to keep the Polyquat up since the higher chlorine levels will oxidize it. Another additional thing you can try is to add borates to 50ppm but borate sources are typically not available in Europe. If algae does show up it will be critical to kill it as quickly as possible and then use a flocc or clarifier (you did not specify any pool size or equipment) to clear the water quickly.

    Some other bad ideas might be - converting the pool to a copper mineral ion pool (possible staining problems) or converting the pool to bromine. A bromine pool will not be affected by high CYA but it will lose bromine at a faster rate than a chlorine pool will lose chlorine. Converting to bromine would easy BUT it is permanent - once a bromine pool, always a bromine pool until the water is dumped.

    As you can see, all of these options are much more expensive and difficult to maintain but they are all you have at this point. Good luck.
    Matt
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    Re: Cant get the FC to hold

    Quote Originally Posted by JoyfulNoise View Post
    Without accurate test results, it's hard to give good advice. But here's a possibility -

    If your friend can clear the pool then try to use liquid chlorine to keep the FC above 15ppm and the pH within normal ranges. Between 15-20ppm, your active chlorine level will be high enough to kill bacteria and viruses by too low for algae control. You will need to use a secondary sanitizer/algaecide to keep the algae under control. If your friend has access to Polyquat-60, that would be a good place to start. It will require regular weekly dosing in order to keep the Polyquat up since the higher chlorine levels will oxidize it. Another additional thing you can try is to add borates to 50ppm but borate sources are typically not available in Europe. If algae does show up it will be critical to kill it as quickly as possible and then use a flocc or clarifier (you did not specify any pool size or equipment) to clear the water quickly.

    Some other bad ideas might be - converting the pool to a copper mineral ion pool (possible staining problems) or converting the pool to bromine. A bromine pool will not be affected by high CYA but it will lose bromine at a faster rate than a chlorine pool will lose chlorine. Converting to bromine would easy BUT it is permanent - once a bromine pool, always a bromine pool until the water is dumped.

    As you can see, all of these options are much more expensive and difficult to maintain but they are all you have at this point. Good luck.
    Many thanks Matt for your suggestions, you have helped me to refine a plan for a way forward. We have now cleared the pool and after the last shock with liquid chlorine the pool is looking and feeling good and the chlorine is holding at last. Using liquid chlorine we can at least calculate what we are adding daily. The pool supply shops up in the mountains of andalucia are not very sophisticated so I'm not sure we will find Polyquat-60 but I'm sure we will find some form of algaecide so we will add that weekly. As there are only two of them using the pool and they are only light users I think using this formula and with daily testing and regular cleaning they should be able to keep the green stuff at bay until they hand the house back in September.

    Sorry I have frustrated those who want a perfect solution, I would have loved one myself but on this occasion it is just not possible sadly.

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    JoyfulNoise's Avatar
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    Cant get the FC to hold

    Careful with algaecides. Demand to know what is in them. Some are copper sulfate based which will add metals to the pool water. Others are either EDTA or bromine based and will cause a huge chlorine demand. Finally, linear quat algaecides (ADBAC) break down very easily from chlorine oxidation and will form compounds that cause foamy water. Polyquat-60 is the only algaecide we recommend because it had the least amount of bad side effects. If you can't find it locally then I suggest looking online to find it. The main ingredient is -

    Poly [oxyethylene (dimethyliminio)ethylen e(dimethyliminio) ethylene dichloride]

    You DO NOT want -

    alkyldimethylbenzylammonium chloride (ADBAC)
    Matt
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    Re: Cant get the FC to hold

    Quote Originally Posted by JoyfulNoise View Post
    Careful with algaecides. Demand to know what is in them. Some are copper sulfate based which will add metals to the pool water. Others are either EDTA or bromine based and will cause a huge chlorine demand. Finally, linear quat algaecides (ADBAC) break down very easily from chlorine oxidation and will form compounds that cause foamy water. Polyquat-60 is the only algaecide we recommend because it had the least amount of bad side effects. If you can't find it locally then I suggest looking online to find it. The main ingredient is -

    Poly [oxyethylene (dimethyliminio)ethylen e(dimethyliminio) ethylene dichloride]

    You DO NOT want -

    alkyldimethylbenzylammonium chloride (ADBAC)
    Ah, many thanks for that I will pass it on. As you say we may have to get it from the internet.

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    Re: Cant get the FC to hold

    I sympathize with your frustrations, both with the pool and how to move forward. And I admire you for trying to help your friend from afar.

    Matt has provided some alternatives, which hopefully are helpful. But until something is done, closing the pool should be considered. Thankfully it's only a month and a half, but your friends deserve to know that the pool does not have enough active chlorine for reasonable pathogen kill times. It might be OK if it's just a married couple and no visitors, but I would certainly not be inviting anyone else into that bath water, or letting my kids swim in it. If I had to go in, I'd wear goggles, nose-clip, and keep my mouth closed. Probably more frustrating and negative advice, but I think it's important. The bromine suggestion is at least somewhat predictable, and would certainly get even with the owners for the shoddy management!

    The CYA buffering system ties up the vast majority of the chlorine, and there's no experience base for CYA levels that high. Even relying on calculating/extrapolating values suggests anything less than around 60% of the calculated minimum will not kill pathogens adequately. No one can give a number for either minimum or maximum safe levels without knowing the CYA number.

    If it were me, I'd be negotiating lower rent for the vacation house and spending the money on swimming elsewhere.

    Finally, the spectre of water shortages usually boils down to money. A letter from a lawyer to the owner might just cause a couple of tanker trucks to roll up.

    Again, good for you for trying to help your friend, and thanks for looking to TFP for help.
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