Operating a high CYA pool

[jgf310]

Hi,


using Leslie test strips, i typically get CYA values of 100-150ppm - the strips are hard to read and the, color change isn't consistent, and i need a better CYA test.., but i think it's safe to say i have a level over 100ppm

I know that to lower CYA i have to partially drain the pool

But, I don't want to do that now. The reason is that i don't have a pool heater, and my pool is currently at 80-82deg F, which my family likes. If i pump out, say 1/2 to 2/3 of the water and replace it, the pool will be cold. I have only 2 or 3 weeks before my kids head off to college, and would like them to be able to use pool til then.

Hence my title - Operating a high CYA pool - I have read that it's possible to do it, but i have some general questions.., and then some more questions about my pool specifically.

1) Will shocking still do anything beneficial? I have read that High CYA pools need to be shocked at higher FC levels - over 25ppm for my CYA. Will shocking at over 25ppm help with the cloramine smell that i get.., or is there something about high CYA levels that just make shocking (at any FC) ineffective for chloramine? How about killing algae? will shocking - again at 25ppm or so - do anything, or, is there something about high CYA that makes shocking ineffective for this problem.

I plan to use liquid bleach to shock

2) if I have high CYA, and I shock to 25ppm.., does the high CYA mean that my FC levels will take forever (days or more) to come down to " normal" levels? I have read that normal for my pool would be FC = 5 to 8ppm.


now, turning to my pool.., first the numbers:

FC - typically 2 to 3
TC - typically 2.5 to 3
CC - typically 0 to 0.5

CYA - 100-150ppm
pH - 7.2 to 7.4
Alk - typically 150ppm

Problems: cloudy water, chloramine (or so i have been told) smell, continual algae growth on walls
my pool gets relatively little use - hardly ever any little kids.., mostly adults and college girls who don't spend much time actually in the pool

from everything i have read.., i should have a higher FC - 5 to 8ppm.., is that correct?

if i shock to 25ppm, and then maintain 5 to 8 ppm, does that have a chance of controlling algae?

should i just bite the bullet and replace the water now.., or can i wait til the end of the season, or the beginning of the next season?

thanks for any help.

jgf

 

[pooldv]

Welcome to TFP!

FC level is set based on the CYA level and the [FC/CYA][/FC/CYA]. So, if your CYA is 150 then add together the 50 and the 100 numbers. In order for a pool to be safe and properly sanitized it must stay above minimum for your CYA at all times. When FC drops below minimum the kill rate for bacteria, viruses, pathogens and algae is too slow to effectively prevent person to person disease transmission and algae growth.

One of the biggest problems with having high CYA and maintaining high FC to compensate for it is that the PH test is not valid when FC IS above 10.

 

[jgf310]

The CYA/Chlorine table on this site has generally higher target values of FC than the table I referenced in my first post

For CYA=100ppm, the table here has 14ppm and 29ppm for shocking, compared with 5-8, and 20-25.

and, i may well be higher than 100ppm CYA...

I can definitely shock it to 29.., but maintaining it at 29 for a slam might not be easy..., and i might need to be higher than that.

I think my next step is to get a better test kit.

Still, if anyone can answer my question about returning from shock FC to normal FC, i would appreciate it.

here it is rephrased - if i have a CYA=100ppm, and i shock to FC=29ppm, and maintain that for a few days til chlorine demand drops off as recommended to slam the pool.., about how long will it take for FC to drop to 14?

my fear is that with such high CYA, and having killed off everything that consumes chlorine.., it will stay high for a very long time.

is that correct?

thanks

 

[Mike1162]

It really doesn't matter how long it takes for the FC to drop back down. The pool is safe to swim in as long as the FC is at or below shock level. However you do need an accurate reading on both CYA & FC. Diluting the pool water 1:1 with tap water may help you get a better CYA reading. Just double the result.

Now to answer your question. After shocking you'll still lose 2 or 3 ppm FC per day.

 

[Texas Splash]

here it is rephrased - if i have a CYA=100ppm, and i shock to FC=29ppm, and maintain that for a few days until chlorine demand drops off as recommended to slam the pool.., about how long will it take for FC to drop to 14?

Just for that question itself ..... if you were to "SLAM" (TFP does not shock) at the required FC of "39" based on the chlorine/CYA Chart until all 3 SLAM criteria passed, then it might take 2-3 days for the FC to drops back to the daily range of 12 based on a CYA of 100. Even still, we can swim as long we do not exceed that SLAM level of 39.

As for this whole scenario though, everything noted above is hypothetical and (at times) tries to mix methodology between TFP levels and other pool industry standards. You can't mix the two concepts, and we really discourage trying to estimate chemical dosages whenever possible. The one thing you have absolutely correct is you need the proper test kit (TF-100 or Taylor K-2006C). But to estimate an FC level to attain sanitation based on a truly unknown CYA will not accomplish anything other than wasting bleach and time.

With one of the recommended test kits noted above, you would be able to perform a "diluted" CYA test to give you a much better idea of your true CYA so that you could adjust FC more accurately.

 

[pooldv]

Normal FC consumption in a pool is 2-4 ppm per day so it will drop by that amount daily, possibly a little more with higher FC. It is safe to swim with FC up to shock level for your CYA. Shock level on the [FC/CYA][/FC/CYA] is less harsh than a public pool with FC of 1 ppm and no CYA. This is due to the buffering capacity of CYA on on the harsh effects FC. We swam every day for nearly a week with FC at 25-28 and CYA at 70 and nobody noticed.

 

[jgf310]

thanks for the responses

yes, i see i misread the table on this site- shock level for CYA=100 is 39, not 29

i can definitely buy enough bleach to do the slam procedure

but i note that shock level for CYA > 100ppm is not given on this site.., so i infer that if CYA > 100ppm, the recommendation of this site is to dilute the pool to CYA < 100ppm before attempting to slam the pool

is that correct?

I will get the better test kit immediately

 

[jgf310]

maybe i spoke too soon - it looks like i will need ~20 jugs of bleach to achieve FC=39ppm.., and what.., maybe another 25-50% of that to complete the slam.., so 30 jugs

that's a lot of bleach...

I guess one answer to the question in my last post is that at CYA > 100ppm, it just becomes impractical

 

[JoyfulNoise]

I guess one answer to the question in my last post is that at CYA > 100ppm, it just becomes impractical

That sums it up.

Trying to operate a pool with very high CYA is tricky. But your situation is different - you're trying to "clean up" a pool with high CYA and that's both very tricky and expensive. I'd bet you use a lot more than 30 gallons of bleach...I'd estimate at least 50 gallons when all is said and done. Also, if your CYA is actually closer to 150ppm, then your shock level of FC is 60ppm (we calculate "shock" levels of chlorine as 40% of CYA). That's above the range of the FAS-DPD test and would require dilution of the sample water to make a reading that high. You will also tear through test reagents pretty quickly with such a high FC. It's just totally impractical to try to SLAM a pool with a CYA over 100ppm.

Also, it is not entirely true that your will lose 2-4ppm per day. In a clean pool (post SLAM) and with a CYA over 100ppm, the UV loss of FC is very low (UV light is the primary component of FC loss without any bather load in the water). You could easily be down at a loss rate of 1ppm/day. So if you started your water off at or near 60ppm FC, it could take well over a week or two for the pool water to drift down on it's own naturally and especially so since your pool water is relatively cold (low 80's).

However, as others have said, this is all just talk until you actually get a good test kit and get some actual pool water data.

 

[jgf310]

I received my TF-100 kit - here are my numbers:

FC=5ppm
CC=0.5ppm

CYA=90ppm

CH=300ppm
TA=135ppm
pH=7.2

while waiting for my kit, i replaced about 12% of my water.

My plan now is to replace water til i am down to about CYA=70ppm. and shock/slam

As I mentioned above.., i don't want to do the water replacement all at once, so it will take a while to get down to CYA=50 or so

I also see that I need to get FC higher - to at least 7ppm - immediately

How does that sound?

 

[max2k]

I received my TF-100 kit - here are my numbers:

FC=5ppm
CC=0.5ppm

CYA=90ppm

CH=300ppm
TA=135ppm
pH=7.2

while waiting for my kit, i replaced about 12% of my water.

My plan now is to replace water til i am down to about CYA=70ppm. and shock/slam

As I mentioned above.., i don't want to do the water replacement all at once, so it will take a while to get down to CYA=50 or so

I also see that I need to get FC higher - to at least 7ppm - immediately

How does that sound?

sounds like you got it I can only add it helps to brush and keep filter 24/7 if you can do it and also take pics of the progress daily over stairs with increasing depth.

 

[JoyfulNoise]

It doable even at 90ppm CYA. But if you want to get it down to 70ppm and then SLAM, that's fine too.

Good luck. Post pics!

 

[jgf310]

Question about the CC number:

i think i have seen this referred to as both Combined Chlorine, and Combined Chloramine.

If i understand correctly.., the chloramine is what gives a pool the "chlorine smell" that everyone hates

Is CC a measure of Chloramine level?

I understand it is supposed to be 0ppm.

Mine is 0.5 - my pool has a terrible smell, and is fighting a bad algae problem.

wouldn't we expect my CC to be even higher than 0.5ppm?

How high can it get?

 

[JoyfulNoise]

Question about the CC number:

i think i have seen this referred to as both Combined Chlorine, and Combined Chloramine.

If i understand correctly.., the chloramine is what gives a pool the "chlorine smell" that everyone hates

Is CC a measure of Chloramine level?

I understand it is supposed to be 0ppm.

Mine is 0.5 - my pool has a terrible smell, and is fighting a bad algae problem.

wouldn't we expect my CC to be even higher than 0.5ppm?

How high can it get?

Something I recently wrote -

“Combined Chorine” is a generic chemical term for chemical compounds formed from the reactions of chlorine with organic and biological contaminants in pool water. Chlorine, and specifically the active chlorine compound hypochlorous acid (HOCl), is a very powerful oxidizer. Oxidizers, in chemical terms, take electrons away from the molecules that they oxidize and, in the process, break those molecules down into different compounds. The most common forms of combined chlorine found in swimming pools are those compounds where chlorine has reacted with nitrogen-containing chemicals in human bather waste (sweat, urine, etc). These chlorine-nitrogen compounds are called “chloramines” and there are three primary types - monochloramine, dichloramine and nitrogen trichloride. Chlorine can also react with urea and form monochlorourea and related compounds. There are many other types of chlorinated organic compounds that can form and not all of them show up on a combined chlorine test. Combined chlorine compounds are extremely irritating to mucous membranes and have fairly low odor thresholds. Combined chlorines are responsible for that “gross chlorine pool smell” and that smell is a good sign that the pool water it is coming from is not being properly maintained. Properly chlorinated pool water with the recommended levels of free chlorine and low to no combined chlorine has absolutely no smell to it…the nose knows, as they say!


High quality pool water test kits test for both FC and CC. Because of the nature of the CC test, it is mostly sensitive to the simple chloramines but not all chlorine-containing organic compounds. Because many CCs are further oxidized and destroyed by UV light and because they are quite volatile compounds (they will naturally outgas from pool water), the CC concentration in a clean swimming pool should be very low (< 1ppm and very often near 0). It is possible to detect high levels of CCs temporarily in pool water and the CC level will fluctuate from time-to-time but any prolonged measure of CCs above 1ppm is indicative of a problem with the pool water being tested. Water that is suffering from an algae and being treated to destroy algae or water that has had a high bather load will often generate lots of CCs while the free chlorine is disinfecting pathogens and oxidizing bather waste. Eventually, though, the CC’s of a clean pool should be below 0.5ppm most of the time.


Some chemical compounds, such as potassium monopersulfate (a common non-chlorine shock used in hot tubs) or sulfamic acid (an organic acid used to remove calcium and metal scale) will show up on the chlorine tests as CCs.

Once you start SLAM'ing, your CC's could still climb higher. It is not unusual at all to get that nasty "chlorine smell" when SLAM'ing a pool.

 

[max2k]

Question about the CC number:

i think i have seen this referred to as both Combined Chlorine, and Combined Chloramine.

If i understand correctly.., the chloramine is what gives a pool the "chlorine smell" that everyone hates

Is CC a measure of Chloramine level?

I understand it is supposed to be 0ppm.

Mine is 0.5 - my pool has a terrible smell, and is fighting a bad algae problem.

wouldn't we expect my CC to be even higher than 0.5ppm?

How high can it get?

In that case you need to SLAM it as soon as you can- no reason to prolong algae suffering You have good kit and you can use PoolMath above to estimate how much chlorine is required to bring your pool to SLAM level. You'll need to brush and run filter 24/7. Please note SLAM is multi- day process and requires you to Maintain SLAM FC level for entire process. With high algae contamination your FC will be dropping quickly in the first hours so stock up on bleach so you won't run out in the middle of it. Test FC every few hrs at the beginning- you'll see yourself how often based on 2-3 of the first tests.