Cya=80 Or Cya=50 & Chlorine Demand

Chlorinating, maintaining the right chlorine levels,
chlorine problems. Dichlor, trichlor, cal hypo, bleach,
granules, chlorine pucks and chlorine sticks.
Henry_R
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Cya=80 Or Cya=50 & Chlorine Demand

Postby Henry_R » Fri 02 Sep, 2011 11:22

I'm now extremely confused by my CYA readings.
I'm using a TF100 kit. When I read the test for CYA I get to around 50 mark and so I read CYA=50.

At two different pool stores where we had phosphates tested both read CYA=80 or CYA=90.
That's fairly consistant for a pool store to read so I'm thinking it might be accurate. We're NOT using anything with stabilizer in it unless the inert 90% portion of chlorine liquid has some unspecified ingredient which it unliklely.

So I'm wondering about something. I've been dosing the pool based on CYA=50, with 1.6 gallons for a FC of 8 but our chlorine drops to almost zero in less than two days. I added 1lb 15oz Cal-hypo 73% at 7:30am Wednesday morning. FC was near 2 with CC=0.5. I didn't check yesterday at all. This morning FC=0.5 on the FAS-DPD test with CC=0. That's a big loss in less than two days with no bathers. We added Phosfree, but phosphates were only 200ppm.

Does this seem consistant with CYA=50 and I'm losing normal chlorine over that span with pH having risen to 8.2 and air temp 100+,pool temp ~80, OR is it possible CYA IS 80 or 90 and I'm only adding 1ppm more than minimum for that CYA amount?

How can I be sure? This is an issue since if the CYA is that high I've obviously not been adding enough chlorine.


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chem geek
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Cya=80 Or Cya=50 & Chlorine Demand

Postby chem geek » Sun 04 Sep, 2011 01:13

Your daily chlorine loss is far more consistent with an CYA level of 50 ppm than 90 ppm. Trust your own readings. Pool stores do not always do tests correctly and often get the CYA test wrong in particular. See this link for what the test should look like. Also note that Taylor recommends standing outside with your back to the sun holding the tube in front of you (with your body shading the tube) looking down into it. That is strong indirect light which is the standard used for this test.

Losing 50% per day at CYA of 50 ppm is on the high side, but not unusual, especially with the very hot weather that you have been reporting. Though a higher CYA level would reduce this loss, it would also require you to maintain an even higher FC level so isn't practical in most manually dosed pools (SWCG pools can get away with it due to their continuous dosing).

Now it is possible for there to be nascent algae growth if the CYA was high and the FC not high enough, but the phosphate remover would have lowered such growth rate so that's why I think it's more likely that your CYA reading is correct and the pool store's readings are wrong.
Henry_R
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Posts: 126
Joined: Fri 20 Mar, 2009 21:41
My Pool: HOA Community Swimming pool built approx. 1971.
In-Ground, Plaster 34x18 3.5-6' deep, Sta-rite P2R A5D-120L pump, A.O. Smith centurion 1HP (uprated 1.25HP) motor,Hayward S244S filter(new 2011), Rainbow Lifegard Chlorine/Bomine feeder; new replastered June 2010
Location: Houston, Texas USA

Cya=80 Or Cya=50 & Chlorine Demand

Postby Henry_R » Sun 04 Sep, 2011 02:42

chem geek wrote:Your daily chlorine loss is far more consistent with an CYA level of 50 ppm than 90 ppm. Trust your own readings. Pool stores do not always do tests correctly and often get the CYA test wrong in particular. See this link for what the test should look like. Also note that Taylor recommends standing outside with your back to the sun holding the tube in front of you (with your body shading the tube) looking down into it. That is strong indirect light which is the standard used for this test.

Losing 50% per day at CYA of 50 ppm is on the high side, but not unusual, especially with the very hot weather that you have been reporting. Though a higher CYA level would reduce this loss, it would also require you to maintain an even higher FC level so isn't practical in most manually dosed pools (SWCG pools can get away with it due to their continuous dosing).

Now it is possible for there to be nascent algae growth if the CYA was high and the FC not high enough, but the phosphate remover would have lowered such growth rate so that's why I think it's more likely that your CYA reading is correct and the pool store's readings are wrong.
See this is what I thought, but it's very strange that multiple people get the same results (CYA=80) including the person whom I do trust at the pool store the mgr. She at least does the tests carefully. I tested CYA myself again under the strongest light I have indoors, my kitchen CFL bulbs which are 60W each and brand new. The test doesn't even begin to get cloudy until well above the 100 mark and settles down at 50. I talked to someone at another pool store whilst searching out something to aerate the pool (going to have to do that sometime, but for now pH and TA are OK though TA is still a little high-140) and was told to let the CYA sample settle fully before doing the test. I had not been letting it settle for long before so this time I let it settle over one minute as the instruction state and I did it three times to be sure I got it. Each time 50 ppm was the result, still. Though looking at the Taylor instructions you linked to, I might not be doing it right. The dot never fully disappears at 50ppm or at all actually. It might be lower actually than 50 ppm (the sample is cloudy but not 100% at the 50 ppm mark), but I sure hope not. :sick:

If it is then I have no way to convince my ignorant neighbors both of whom control the money (one of whom doesn't care, the other one is just gullible that all people at the pool store(s) are "experts") to make adjustments to the CYA.

Interesting you say possible nascent algae. I'm testing for just that though I may have to do it more than once since we have high winds tonight blowing debris around and into the pool and likely skewing the test.

I'm checking to see if the FC goes down over night. I tested it at FC=1.5, CC=0.5 so it's low, but I want to know if we lose all of the remainder or part of it by morning.

Our chlorine demand is such that I'm now taking flak for supposedly using too much chlorine. Does 1.6 gallons of 10% chlorine every other day or so seem too much given the weather, CYA all other things being equal?
The FC target I'm shooting for each time is 8 ppm (high end of FC scale for CYA=50) so as to not have to dose every day. This takes 1 gallon plus 10-8oz cups of liquid (pool calculator numbers) since FC drops so low
by the time I add it.

We have had some high wind conditions today and there are a lot of leaves and some dirt in there now.
I'll vac in the morning to remove some of this too. I vac'd yesterday morning early too, btw.
This debris burns up chlorine too doesn't it? So I might need to do this over night test more than once.

*edit*
This morning I vac'd, scooped leaves and tested the water before adding chlorine.
TC=1.5
FC=1
CC=0.5
pH=>7.5 Hard to tell but not dark enough to be 7.8.

Does losing 0.5ppm at night indicate the presence of bacteria or nascent algae?
I forgot to check last evening and I ended up checking at almost 2am.
At that time
TC=2
FC=1.5
CC=0.5

Now at 8:30am I lost 0.5 ppm with no loss or increase of CC.
Now to be clear there were lots of leaves and some windblown dirt in the pool from high winds yesterday and last night. Can this account for the FC loss?

I just added 1.5 gallons of 10% chlorine and I'm going to check this again tonight.

BTW, how many tests for chlorine does a typical TF100 kit yield? The FAS-DPD test, not just the OTO since the chlorine is beyond the OTO ability. Assuming testing once daily. I'm sure I have plenty, but I'm taking flak
for using "too much".
Money talks!? All it ever says to me is "goodbye!".
chem geek
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Cya=80 Or Cya=50 & Chlorine Demand

Postby chem geek » Sun 04 Sep, 2011 12:17

The test is difficult because it is visual and your mind plays tricks on you thinking that you still see a dot. You can pour the sample from the tube back into the bottle and try again. Doing this a few times, I think you will narrow down to where the dot seems to first disappear. I'd count that as the right amount. There are standard samples you can get for the various tests including the CYA test , but I don't think you need that.

Yes, the overnight chlorine loss test is the way to know if you have non-visible nascent algae or other organics in the pool consuming chlorine.

As for normal chlorine demand, it varies by pool, but is usually somewhere between 1.5 and 3 ppm FC per day with most having around 2-2.5 ppm FC per day. This assumes that the FC starts out at around 10% of the CYA level and that the CYA level is high enough to protect the pool in sunlight. So going from 7 ppm FC to 4 ppm FC with 50 ppm CYA would not be unusual. Your demand is higher than that, most likely due to the higher temperatures, strong sunlight, and people in the pool. In 20,000 gallons, one person-hour would consume around 0.05 ppm FC so 10 people would be around 0.5 ppm FC unless someone urinates in which case it would be much higher. Anyway, see what your overnight chlorine loss test tells you. If the loss is well less than 1 ppm FC (say, 0.4 ppm FC in 8 hours), then it's mostly the sunlight, again implying that your CYA is most certainly not at 80+ ppm.

Debris does use up chlorine -- pollen is especially bad, leaves less so though enough of them can create noticeable demand as well.

1 gallon plus 10 cups of 10% chlorine in 20,000 gallons would be 8.1 ppm FC. So for 2 days that would be 4 ppm FC per day which is high, but then you are starting out higher and the loss is proportional. If you added chlorine every day starting at 6 ppm, you would probably lose 3 ppm FC each day. If you wanted to add more CYA, you could go back to using Trichlor pucks at least for a while. For every 10 ppm FC added by Trichlor, it will also increase CYA by 6 ppm. It's possible that your CYA might be somewhat lower than 50 ppm -- that would explain the higher chlorine loss, but again let's see what the overnight (no sunlight) loss tells you.

Losing 0.5 ppm FC overnight is good. You should use the 25 ml sample size to get more precise about this since the loss may only be 0.4 ppm or even 0.2 ppm. This does seem to indicate that the bulk of the loss is during the day from sunlight and that perhaps your CYA is too low -- maybe it's only 40 ppm and not 50 ppm.

The TF-100 FAS-DPD has 2 ounces of reagent. There are 24 drops per ml with that dropper tube so that's about 1420 drops. With a 10 ml sample size and say typical 4 ppm FC reading, so 8 drops, that's 178 tests or roughly 6 months. I'm not sure of the size of the scoop of DPD powder, but suspect that it will last longer.

If you add up the kit refill costs plus your chlorinating liquid and acid (for now -- it will lower over time), it should still be a lot less than they were paying for someone to maintain the pool poorly with that green. You might run some calculations to show them how you are actually saving them money. At 13 cups of chlorine per day (which is high, but let's use that), this is 24 gallons per month which at $3 per gallon would be around $75 which is less than the $100 per month they were charging. Once you get your chlorine usage down to closer to 2-3 ppm fC per day, you should be at $50 or less per month.
Henry_R
Swimming Pool Pro
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Posts: 126
Joined: Fri 20 Mar, 2009 21:41
My Pool: HOA Community Swimming pool built approx. 1971.
In-Ground, Plaster 34x18 3.5-6' deep, Sta-rite P2R A5D-120L pump, A.O. Smith centurion 1HP (uprated 1.25HP) motor,Hayward S244S filter(new 2011), Rainbow Lifegard Chlorine/Bomine feeder; new replastered June 2010
Location: Houston, Texas USA

Cya=80 Or Cya=50 & Chlorine Demand

Postby Henry_R » Sun 04 Sep, 2011 13:23

chem geek wrote:The test is difficult because it is visual and your mind plays tricks on you thinking that you still see a dot. You can pour the sample from the tube back into the bottle and try again. Doing this a few times, I think you will narrow down to where the dot seems to first disappear. I'd count that as the right amount. There are standard samples you can get for the various tests including the CYA test , but I don't think you need that.

Yes, the overnight chlorine loss test is the way to know if you have non-visible nascent algae or other organics in the pool consuming chlorine.

As for normal chlorine demand, it varies by pool, but is usually somewhere between 1.5 and 3 ppm FC per day with most having around 2-2.5 ppm FC per day. This assumes that the FC starts out at around 10% of the CYA level and that the CYA level is high enough to protect the pool in sunlight. So going from 7 ppm FC to 4 ppm FC with 50 ppm CYA would not be unusual. Your demand is higher than that, most likely due to the higher temperatures, strong sunlight, and people in the pool. In 20,000 gallons, one person-hour would consume around 0.05 ppm FC so 10 people would be around 0.5 ppm FC unless someone urinates in which case it would be much higher. Anyway, see what your overnight chlorine loss test tells you. If the loss is well less than 1 ppm FC (say, 0.4 ppm FC in 8 hours), then it's mostly the sunlight, again implying that your CYA is most certainly not at 80+ ppm.

Debris does use up chlorine -- pollen is especially bad, leaves less so though enough of them can create noticeable demand as well.

1 gallon plus 10 cups of 10% chlorine in 20,000 gallons would be 8.1 ppm FC. So for 2 days that would be 4 ppm FC per day which is high, but then you are starting out higher and the loss is proportional. If you added chlorine every day starting at 6 ppm, you would probably lose 3 ppm FC each day. If you wanted to add more CYA, you could go back to using Trichlor pucks at least for a while. For every 10 ppm FC added by Trichlor, it will also increase CYA by 6 ppm. It's possible that your CYA might be somewhat lower than 50 ppm -- that would explain the higher chlorine loss, but again let's see what the overnight (no sunlight) loss tells you.

Losing 0.5 ppm FC overnight is good. You should use the 25 ml sample size to get more precise about this since the loss may only be 0.4 ppm or even 0.2 ppm. This does seem to indicate that the bulk of the loss is during the day from sunlight and that perhaps your CYA is too low -- maybe it's only 40 ppm and not 50 ppm.

The TF-100 FAS-DPD has 2 ounces of reagent. There are 24 drops per ml with that dropper tube so that's about 1420 drops. With a 10 ml sample size and say typical 4 ppm FC reading, so 8 drops, that's 178 tests or roughly 6 months. I'm not sure of the size of the scoop of DPD powder, but suspect that it will last longer.

If you add up the kit refill costs plus your chlorinating liquid and acid (for now -- it will lower over time), it should still be a lot less than they were paying for someone to maintain the pool poorly with that green. You might run some calculations to show them how you are actually saving them money. At 13 cups of chlorine per day (which is high, but let's use that), this is 24 gallons per month which at $3 per gallon would be around $75 which is less than the $100 per month they were charging. Once you get your chlorine usage down to closer to 2-3 ppm fC per day, you should be at $50 or less per month.
I'm going to try testing it outside next time. I watched the videos at Taylor's website and I can say for sure I've *never* had the dot totally disappear the way their video shows when I've done the CYA test. It's always somewhat visible. And moving the sample seems to make it change some too.

OK, that's what I thought about the reagents, titrants etc. These bottle are the same size (except the CYA reagent) as the Taylor 2005 Leslie's sells and that kit lasted long enough that the chemicals expired from lack of use and age. I seem to remember refilling the DPD reagent though, but the rest lasted very long.

I hope to begin dosing daily vs every other day. The powers that be though seem to think letting the chlorine bottom out then redosing is the way to go however so I'm not being given access to the chlorine as needed.

I do think that the CYA is a little lower than I'm reading as I've said I'll try it in sunlight next time, but how to convince an uncaring, ignoramous of same? :rant: The pool stores as I've said are reading far higher 80-90 and so my test is rendered moot. :rant:

The 10% liquid chlorine is about $3.79 per gallon with 8.25 sales tax added vs $3.23 also tax added for 6% unscented bleach from walmart in a 182 oz bottle. I think there might be a small cost reduction to buy the 6%. Maybe $1 or so per use due to larger qty even though the dose it higher. I'm not sure how to figure that out. Numbers are not and never have been my thing.... :oops: If there is perhaps I may consider having them get that. They want to use cal-hypo perceiving it as cheaper. My last CH test read something 370.
If we start using cal-hypo it's going to rise. I may need to do that for a short time to please those in charge.
WE already have scaling and dust sticking to the walls which when brushed clouds the water.
The ignorance of the people here is appalling. They believe that merely brushing the walls, letting it settle then vacuuming it out will lower CH or keep it in check. That doesn't sound right? I thought only dilution would lower CH?

The costs *should* be lower to do this ourselves, but we've already spent the better part of $500 or more since August on supplies.

It had to have been at least $300 on the trichlor tab (which we're not using anymore and are sitting around) and 50lb bucket of cal-hypo 73%(Leslie's Pool brand) and the pole, vacuum hose and vacuum head. Not to mention clarifier (leslie's clear brite(sp?)) once, No Mor Problems, Alum (tossed in for free the first time,
$$ the next. Used both times WITHOUT following the directions to lower pH first so it worked only partially).

Then 6 boxes 4-1 gallon jugs of liquid 10% chlorine at $13.99 each box. This doesn't include the water bill for the partial drain/refill twice, and extra electricity for running the pump continuously several times. Gas mileage which the manager and board members are reimbursed at $0.50 per mile.

We've spent the better part of three months worth of pool service fees (the man was only charging $160 per mo.) in 8 weeks.

Anyway this looks like it's a lot, but I think you're right it's not as much as we would be spending on a pool service. Now if they would just realise the pool store is not be-all, tell-all this would be even less expensive.
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chem geek
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Cya=80 Or Cya=50 & Chlorine Demand

Postby chem geek » Sun 04 Sep, 2011 22:25

Are you sure that's not a 192 ounce bottle of bleach (that would be 1.5 gallons which is more typical for the larger size bleach bottles)? Anyway, if it is 182 ounces, then the way you compare is the dollars per % per volume, though bleach is technically 6.17% available chlorine by volume (it's 5.7% by weight). ($3.23/6.17)/(182/128) = $0.37 per gallon per %. $3.79/10 = $0.38 per gallon per %. So it's pretty much a wash between the two. The chlorinating liquid is more convenient since it's more concentrated so less weight to carry.

Since you have Trichlor tabs and likely have a lower CYA, you could use those to at least give yourself a break from the daily schlepping. For every 10 ppm FC, it will increase CYA by 6 ppm. So at your rate of chlorine usage, you could do this for a week or two and see if the daily chlorine demand drops some from the CYA being somewhat higher. I don't understand how the pool stores are getting such a high CYA reading unless they aren't competent.

Also note that as the TA is lowered, the higher CH will be less likely to scale and also your pH won't rise as much -- you are already seeing some of this effect already.

As for costs, a lot of that was due to months of neglect by the pool service. The continued use of stabilized chlorine got the CYA level very high making the chlorine less effective. They could have compensated for this (at extra cost) by use of algaecides, phosphate removers, etc. but it's generally better to keep the CYA in check. The problem is that it isn't as convenient -- there aren't chlorine tabs that don't add either CYA (Trichlor) or CH (Cal-Hypo).

Chlorine is a consumable and were it not for slow-dissolving Trichlor tabs it would have to be added every day in hot weather or perhaps every other day. Your HOA is wrong to think it is better to have wider swings of chlorine levels. It is more efficient to keep a steady level which is why commercial/public pool systems use peristaltic pumps and many homeowners and condos use saltwater chlorine generators.

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