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Thread: Rising combined CHL level

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    Rising combined CHL level

    Can somebody help please?

    I have a canine Hydrotherapy pool which holds 9,000 litres (2,000 imperial gallons). It is indoors above ground and made of Polypropylene and has a sand filter. The pump will circulate the water volume in an hour but obviously takes about 3 - 4 hours for complete water turnover.
    I have to admit however that the pool is not running 24/7 as I do not have dogs in every day for rehab. One day a week it is not on at all.
    The problem I have is that I have over the last week the combined CHL going higher than it ever has done. It is normally under 1.0 but is now at 1.66 and rising. Free CHL is supposed to be between 1 - 3ppm for dogs in this pool. ALK has been a bit low and I have just managed to get it up to 104 today. I like it between 80 and 120. Water hardness has also been a bit of a problem and today it is at 172 although I would like it higher I will be adding more calcium in the morning.
    I use chlorine granules which I dissolve in a bucket of warm water before emptying round the edges of the pool. The water temperature is a constant 29.5 C to 30C heated by a hot water heat pump (very economical!)
    What I want to know is how much chlorine should I be adding to this pool to get rid of the high combined CHL levels?
    Help would be gratefully appreciated
    9,000Ltr indoor above ground polypropylene canine hydrotherapy pool http://www.4wetpaws.co.nz

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    Rising combined CHL level

    Sorry forgot to say that the water has always been clear, no signs of algae etc. no 'chlorine' smell however; the chlorine level has dropped lower than 1 a few times over the last couple of weeks when there has been no dogs in the pool.

    Tawa
    9,000Ltr indoor above ground polypropylene canine hydrotherapy pool http://www.4wetpaws.co.nz

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    Re: Rising combined CHL level

    Welcome to TFP!

    I merged your two posts so that the thread stays together. In the future, if you need to add information, either edit your original thread or add a new post to the same thread.

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    Re: Rising combined CHL level

    Welcome to TFP!

    When you say that you use "chlorine granules", can you please be more specific? Look at the ingredients -- does it say "Calcium hypochlorite" and if so, what concentration, or does it say "Sodium dichloroisocyanurate dihydrate" or "Sodium dichloro-s-traizinetrione dihydrate"? What is the Cyanuric Acid (CYA) level in the water? You noted in other threads that you are using the ColorQ and we know it may have problems reading higher CH levels, for example.
    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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    Mod Squad jblizzle's Avatar
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    Re: Rising combined CHL level

    Welcome to TFP!!!

    Maintaining a canine hydrotherapy pool is not different than maintaining any other pool ... beside maybe a need for a little more chlorine.

    You can find out all about the chemical levels we recommend in Pool School.

    Really to know how much FC you need, you have to know the CYA level ... and I think that is one of the things the ColorQ is not as good at.

    Being indoors, you do not need much CYA, but maintaining a CYA level around 20ppm buffers the FC and makes the water much less harsh with lower active chlorine levels.

    As Chem Geek asked, what kind of the powdered chlorine are you using? Some add calcium and others add CYA ... would be easier to switch to liquid chlorine if you are adding chlorine every 1-2 days.
    Jason, TFP Moderator
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    Re: Rising combined CHL level

    Weclome!

    as above, we need to know what type of Chlorine Granules you use, it may be that you are using Di-chlor granules which have been steadily increasing your CYA level, or you may not have any stabiliser present if you use Calcium Hypochlorite.

    Do you have a way of testing your Cyanuric Acid level, as this is an important measure which is missing from your thread. Once we have more details we can most certainly assist however!
    Stuart Murray
    Scotland UK
    UK NPPOC

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    Re: Rising combined CHL level

    Oh dear thanks for that guys. I have for some reason never tested for CYA as pool indoors and not getting any UV from the sun.
    I have just tested it and it is 7ppm
    What will I need to add to get it to your recommended 20?
    Also I have read and read again the labels on the chlorine and it is Crystal Water brand and only says it is Calcium Hypochlorite, it does not give the % of it.
    All my other reading this morning are as follows
    FC 1.69
    TOTAL CHL 3.22
    Combined 1.58
    PH 7.6
    ALK 110
    CH 185

    I don't have any dogs booked in today but 2 on Friday afternoon. I don't think that I will have time to put a large amount of CHL in to shock and for the level to be back down in time. I am able to do it on Saturday as there will be three days of no dogs as the pool is closed
    9,000Ltr indoor above ground polypropylene canine hydrotherapy pool http://www.4wetpaws.co.nz

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    Re: Rising combined CHL level

    Is your source water soft, with low pH, TA, CH? I ask because you are using Calcium Hypochlorite (You can test your water which helps you understand the effects of adding supply water to your pool.

    As for the CYA it is not essential in Indoor Pools but definitely helps maintain the Chlorine Residual and I would advise for any residential or canine indoor pool! You can add Cyanuric Acid (Sometimes called stabiliser), or chlorinate with Tri-Chlor tablets or Di-chlor Granules to increase the CYA level.

    Meantime, you really need to shock to get rid of the Chloramines (CC's) in your pool, but as an absolute minimum you need to maintain your FC residual above the level of the CC's. If I were you I would shoot for around 10ppm FC until Saturday (Still safe for bathers be it Human or Canine) then start your shocking of the pool. Remember shocking the pool is a process of maintaining the shock level until you pass certain criteria, which for you would be 0.5ppm or less CC's, clear water and the pool losing less than 1.0ppm FC. Detailed instructions for shocking are on the link below.

    pool-school/shocking_your_pool
    Stuart Murray
    Scotland UK
    UK NPPOC

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    Re: Rising combined CHL level

    Thanks Stuart,
    Tap water results tho not sure what to make of them!! Our water currently comes from a reservoir up in the hills behind us. Due to the drought we have had over the summer and then a lot of rain this last week it is sure to have effected the water balance. We used to never be able to get a good lather with soap and now I have bubbles everywhere when washing up!
    FC 1.07
    TCL 1.11
    PH 7.7
    ALK 27
    CH 40
    I have just added some PH decrease and in a while will add some CHL to get it up to 10ppm.
    Given the results of the tap water what do you suggest I use for sanitising other than what I already use?
    9,000Ltr indoor above ground polypropylene canine hydrotherapy pool http://www.4wetpaws.co.nz

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    Re: Rising combined CHL level

    You have soft surface water, very similar readings to here in Scotland and Calcium Hypo is ideal for soft water as rising CH levels is not usually a problem (the Cal Hypo is the only real source of CH increase), you could switch to bleach but I'd be sticking with what I'm using unless CH gets too high and I don't see that issue with your numbers.
    Stuart Murray
    Scotland UK
    UK NPPOC

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    Re: Rising combined CHL level

    Hi Stuart,
    I tested the water, the FC was Hi so obviously over 10ppm. (added too much CHL!) Tested again at 5pm and it was down to 9.45. TCL hi. Have just tested again at midnight and only down to 9.26 and TCL still HI. I have emptied out about a foot of water and refilled and will not test again now until morning. If the readings for TCL are showing figures other than HI should I start to try and raise the CH and ALK despite the CHL level still being up there as I only have tomorrow (Friday) to get it sorted out as I cancelled the dogs and moved them to come on Saturday in the hopes that balance would be better. Can I just confirm that it is better to get the CH level up before the ALK?
    The ALK was down to about 40 when I tested at 5pm so didn't bother at that time doing the CH as it was obviously going to be right down too!
    9,000Ltr indoor above ground polypropylene canine hydrotherapy pool http://www.4wetpaws.co.nz

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    Re: Rising combined CHL level

    I presume you are using a photometer with those results? I would be working off the Fibreglass Recommended levels for your pool which are
    FC 3-7
    pH 7.5-7.8
    TA 70-90+(120)
    CH 220-320
    CYA 30-50 (Indoor 0-40)
    Shock level for 7 CYA is around 8-10ppm FC

    Keep your FC around that level until it kills off the CC's so your TC is 0.5ppm or less higher than your FC reading (it's highly unlikely you will get 0.0CC in an indoor pool,) Try to maintain good ventilation also as this will assist in reducing your CC's 8-10ppm FC is perfectly safe to continue use.

    It's not ideal but you can do a dilution test of 1:1 Pool/Non chlorinated water (bear in mind tap water has Chlorine present so Bottled or Sterile water) to measure your chlorine residual in the absence of an FAS-DPD test kit. (try to mix your water in a 20/50ml syringe to try to keep it as close to exact measurements as possible, the readings you achieve should then be doubled.

    It is best to get FC then TA/pH sorted out first then the rest, so I would slowly start raising TA with Bi-Carb and acid addition, but the lack of TA is no biggie, I don't know what % of water you have replaced but your CH will have dropped also, but with the shocking and (presumably) lack of grout/plaster I would be in no rush to correct CH levels, and the Calcium Hypochlorite shall gradually increase the CH level anyway.

    CYA can be increased after you have finished the shocking process, you don't really want a lot of CYA holding the chlorine indoors until you finish the shock porocess, then you can increase CYA (I usually go for around 35ppm CYA in indoor pools as I find this gives a real good level of stability)

    Don't worry about any more water replacement, with soft water you are only going to drop TA, CH and increase CC's (given the organics which come in from surface water and the odd fish having a pee further upstream just maintain shock level of between 8-10ppm until you pass these 3 targets:
    Clear Water, CC's of 0.5ppm or less and an overnight chlorine loss (sunset to dawn) of 1.0ppm FC (further details in the following thread
    pool-school/overnight_fc_test
    Stuart Murray
    Scotland UK
    UK NPPOC

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    Re: Rising combined CHL level

    2 out of 3 targets met, the water is crystal clear, always has been and the FC went from 9.26 last night to 7.99 this morning so just the CC's to get rid of which are still 1.26. (Yes I have a colorq pro 7 photometer)
    I'm sorry I am such a nuisance but chemistry was never my strong point, but do I have to add more Calcium Hypo now to get CHL back up to 10ppm?
    9,000Ltr indoor above ground polypropylene canine hydrotherapy pool http://www.4wetpaws.co.nz

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    Re: Rising combined CHL level

    the FC went from 9.26 last night to 7.99 this morning
    the criterium we use is a .5 ppm loss or less so you're not quite there.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: Rising combined CHL level

    Maths not good either then!!! So do you want me to add more CHL ?
    9,000Ltr indoor above ground polypropylene canine hydrotherapy pool http://www.4wetpaws.co.nz

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    Mod Squad jblizzle's Avatar
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    Re: Rising combined CHL level

    You should maintain the FC at the shock level for your CYA ... since your CYA appears to be < 20ppm, you should try to maintain a FC of 10ppm until ou pass the 3 tests to stop the shock process:
    pool-school/shocking_your_pool

    BUT, we have no way of know how accurate your meter is ... so will it really know when the CC is < 0.5ppm and the FC drops by less than 1ppm over night?
    Jason, TFP Moderator
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    Re: Rising combined CHL level

    Quote Originally Posted by duraleigh
    the FC went from 9.26 last night to 7.99 this morning
    the criterium we use is a .5 ppm loss or less so you're not quite there.
    For overnight loss it's 1 ppm FC or less. The 0.5 ppm or less is the criteria for Combined Chlorine (CC). At any rate, the loss rate still seems too high overnight.
    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: Rising combined CHL level

    Overnight you lost just over 1ppm FC so that's not a biggie especially in an un-stabilised pool, just maintain your shock level of between 8-10ppm and allow it to burn off the CC's till they are reading 0.5ppm or less and you will be good, remember the dogs will be fine swimming in FC at your shock level so you can maintain shock level and continue use - your doing grand!
    Stuart Murray
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    Re: Rising combined CHL level

    I would just like to publically thank Stuamurr for all his advice both on this forum page and through private messaging and help with the problems I have been having with my pool water. He has managed to keep me sane and together we have just about cracked the problem. This Forum is lucky to have his input and sound sensible advice. Thank you Stu.
    9,000Ltr indoor above ground polypropylene canine hydrotherapy pool http://www.4wetpaws.co.nz

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