Very High CYA level requires high chlorine level - is it safe?

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surf3fin

0
Oct 1, 2014
7
Norco, CA
I am a new member and must start with saying thank you for providing such a great site with excellent information. Now on to my question:
I have a 40,000 gallon in ground plaster pool in Southern California with a DE filter on it. I bought this house and the pool was already in place so I have no idea how long the water has been in it. The CYA level is very high - 250 according to the tests done at the local pool supply store. According to the charts posted here I calculate that I need to keep a FC level of 17 min, 30 target, and 100 shock. Is it safe to swim in the pool with FC levels up to 30? The local pool store folks don't seem to acknowledge a relationshop between FC and CYA so they say don't swim if the FC is over 5. Also how do I find a test kit that will register FC levels this high? I have been doing a dilution of the sample with distilled water to get readings over the 5 that my test kit tops out at. I do this by mixing pool water with distilled water in measured amount then running the test and then the math. If I have 25% pool water in the test then I take the ppm result times 4 to get my FC level.

Wow, I guess I have a lot of questions but I will stop for now and again i REALLY APPRECIATE ANY HELP YOU CAN PROVIDE.

Current pool chemistry:
FAC - 6
CH - 230
CYA - 250
TA - 80
pH - 7.5
TDS - 1700
Phosphates - 300

I have been recently using liquid chlorine and muratic acid but was previously using tabs in a floater (this forum told me about those increasing CYA so I switched)

Thanks again,

Norm
 
Hi Norm,
To Start, Welcome to TFP! :)

You are already wayyyy ahead by having read pool school right off the bat.

Most everyone here will recommend the TF-100 test kit. You can get one at this link.
www.tftestkits.net . This test kit will test FC to 30 and way above.

Next, just because everyone else will tell you too, is that no one here trusts pool store testing. They are prone to inaccuracy, as well as the advice of pool store people. Almost all of them dont have their own pool and to he honest,
their knowledge base is basically what a fast talking pool chemical salesman or company tells them.

Things are different here. Everyone here offering advince owns a pool, we have lived and learned, and the TFP method of pool care is based on science and is proven to work, and no one here wants to sell you anything.

If you get a recommended test kit, and keep learning and asking questions here, you will easily enough be able to kick the pool store to the curb.

Dont worry about TDS and Phosphates, those will be of no concern as long as you can maintain your FC vs CYA regardless of what the pool store says.

It IS safe to swim in a pool with FC higher than 5. It would be true if your CYA is 0, but as you know, the pool store folks dont acknowledge the FC - CYA realationship.

It is safe to swim up to FC Shock Level given whatever your CYA is.

I hope this helps,
 
Here is my answer based on a similar situation - The CYA is commonly introduced by those chorine tabs we float in the pool to maintain chlorine levels between shock treatments. Overtime trhe CYA builds up. When my CYA level was high the pool supply clerk said based on my measurements if I was running a puiblic pool they would shut me down. He says high CYA levels reduces the efficiency of the pool chemical treatments to stabilize the pool. When you drain and refill the pool they tell you to use a pool conditioner that raises the CYA levels from zero but low enough to not be a concern. It was a problem for me when I was dealing with an algae outbreak. I think you should drain the pool and start over. There is nothing to bring CYA levels down but a refill - winter time will be here soon so that is a good time to do it.
 
You will want to do at least partial drain/refills to lower your CYA level, but in the meantime maintaining a higher FC level will prevent algae growth. If you truly have 250 ppm CYA (you should double check that measurement yourself with your own proper test kit -- doing dilution with tap water since the kit only measures to 100 ppm), then 7.5% of 250 is 19 ppm (not sure how you got 17 ppm) and this has the same amount of active chlorine (hypochlorous acid, HOCl) as 3.25 ppm FC with 50 ppm CYA.

With 19 ppm FC and 250 ppm CYA, 99.65% of the chlorine is bound to CYA. Now we normally consider it essentially inactive, but at most it may have 1/150th the oxidation power of HOCl so perhaps adds 0.13 ppm to the 0.03 ppm HOCl (unclear if this applies to algae prevention and it probably does not apply to pathogen disinfection) so is equivalent to 0.33 ppm FC with no CYA. While higher than our standard recommendations, this is still very safe. The only issue with a high FC level were if you drank the pool water in large quantities. The EPA limit of 4 ppm FC for drinking water assumes 2 liters or quarts per day so at 19 ppm that would be 13-1/2 fluid ounces per day. You shouldn't be drinking such quantities of pool water, certainly not for a lifetime, and even then only increasing cancer risks by roughly 1 in a million in terms of EPA limits.
 
Thanks folks. This is all great information and I will start with purchasing a good test kit as recommended. I must say that the pool store tests have shown some very strange fluctuation in some of the numbers which give me cause to wonder about their accuracy.

Thanks chem geek for the formula to calculate the CYA to FC ratio. I came up with 17 based on a best guess extrapolation from the chart on this site but having the true CYA # first and the formula (7.5% of CYA level) will put me right on target. Could you provide me with the formula for the slam level of FC also?

I am now retired so have the time to take care of the pool myself but have started without much pool knowledge. Knowledge is the key to being able to take care of this myself and this site is a great place.

I will be taking on the project of a drain and refill this winter and will likely put one of the epoxy type coatings on the pool during that process. In the mean time I will keep it running right by adjusting the FC level to match up with the actual CYA level I determine from the test kit I am ordering today.

Thanks again for all the help.
 
Thanks again. I agree and do not plan to do a slam until after I can do the drain, coating, and refill. In the meantime I have good looking water and good algae control with an FC level at 19. I ordered the good test kit last night and will know what my CYA level really is as soon as it arrives.
 
Dave and Richard have answered your questions, so I figured I'd just jump in and Welcome you to TFP.

I am not surprised that the pool store does not acknowledge the relationship between CYA & FC. Plus they gave you the stock answer not to swim above 5 ppm FC.

I started close to 250 CYA myself (remember, diluted tests are never extremely accurate) and through being quick to backwash, vacuuming to waste regularly and harvesting rainwater I have been able to reduce it to 70. I'm not sure of how the rain situation is in your area, but if you can direct a gutter downspout or two to the pool (you want to filter solid out with a skimmer liner or something similar) you end up with additional free water.
 
This is a great forum and I really appreciate all the advice. I have received the test kit that I ordered and have performed all of the tests twice. Once the day the kit arrived then again today (after taking my sample water inside and letting everything get to the same temps. I am seeing a significant difference in several areas from what the local pool store provided with their free water testing. I guess you really do get what you pay for.

I have charted the test results and have them below along with a follow up question.
Pool Water Numbers


Date
Source pH FC CH CYA TA Pho TDS
6/20/2014Pool Store 7.40 250 60901,000+1,400
7/6/2014Pool Store7.422201001001,000+1,450
8/10/2014Pool Store7.42?250903001,500
8/14/2014Pool Store7.42?100802001,500
9/23/2014Pool Store7.44230250803001,700
10/8/2014DIY7.522850120190??
10/10/2014DIY 7.3518725140130??

Added table to house test results to make it easier to read -BoDarville, TFP Moderator

Original Data Preserved
Date Source pH FC CH CYA TA Pho TDS
20-Jun Pool Store 7.4 0 250 60 90 1000+ 1400
7/6/2014 Pool Store 7.4 2 220 100 100 1000+ 1450
8/10/2014 Pool Store 7.4 2 ? 250 90 300 1500
8/14/2014 Pool Store 7.4 2 ? 100 80 200 1500
9/23/2014 Pool Store 7.4 4 230 250 80 300 1700
10/8/2014 DIY 7.5 22 850 120 190 ? ?
10/10/2014 DIY 7.35 18 725 140 130 ? ?


I plan to drain, coat, and refill the pool this winter and am just trying to keep it going till then as living in So Cal I still have about a month of swimming available. Other than keeping the FC level in line with the CYA level is there anything else that you would recommend?

I am pretty sure that I added to the CH level by using the Power Powder they recommended to shock the pool and to help keep the FC in shape.
I am also pretty sure that the phosphate removal chemicals they sold me did little but provide a nice profit to the store.
I also find the bounce in the CYA level when they were doing the testing very interesting as everything I read says that CYA does not leave a pool unless it is drained out and fresh water replenished behind it.

I would love to use the rain gutter method of flushing the pool but So Cal is in a drought and if I see 4 to 6" of rain in a year it would be a bunch.

Thoughts - ideas- comments???

Again thank you all for providing such a great service and good information. The test kit you recommended is the bomb! I did have to do the CYA test as a diluted test but 15ml of pool water mixed with 15ml of distilled water seems to work well and the results are pretty consistant.
 
Last edited by a moderator:
surf3fin said:
I am also pretty sure that the phosphate removal chemicals they sold me did little but provide a nice profit to the store.
Click to expand...
It did, but I would look at it as a one time cost and chalk it up to the cost of learning.

surf3fin said:
I also find the bounce in the CYA level when they were doing the testing very interesting as everything I read says that CYA does not leave a pool unless it is drained out and fresh water replenished behind it.
Click to expand...
What you have read about CYA being relatively stable unless a substantial drain & refill is done is correct. The bounce in CYA results from the pool store is typical...I've experienced it myself when I was new to TFP. It's a great example of why we recommend DIY testing with the proper test kit - which you are now doing. :goodjob:

The CYA test is the most subjective of the parameters that we recommend testing. I would suggest checking out these Extended Test Kit Directions. The CYA test is described in Post # 8.
 

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Yup,

You are seeing the results o pool store testing. TDS is their way of selling you more snake oil.

Watch your CYA and FC like a hawk. pH and to a lesser extent CH & TA to make sure things runs smoothly with no. scaling.

Lots of swimming and adult beverages;)
 
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