# Thread: Proper TC to FC ratio and CYA numbers

1. ## Proper TC to FC ratio and CYA numbers

Getting ready to close my pool. Just tested by pool installer. TC is 10.0 (I think their test system will not register above 10.0 but I think TC is above 10), FC is 10.0 (but again I think limited by test system), pH is a 7.7, TA is 165, CH is 300, CYA is 135. Reading the TFP Pool School items leads me to believe the TC should be less than .5 while the FC should be about 3.0 and CYA should be about 50. Should I plan on replacing about one half my water come Spring while opening and if I do, will the TC to FC ratio come in line?

2. ## Re: Proper TC to FC ratio and CYA numbers

Welcome to TFP!

If your CYA is actually 135, then yes you will need to plan on a large water replacement in the spring.

We do not have a FC/TC "ratio", but do have a FC to CYA ratio.

I think you are confusing TC with CC. We generally don't talk about TC. We worry about FC and CC, the total of the two is TC.

Everything we teach is predicated on accurate testing and only adding what the pool needs when it needs it.

Before next spring if you are going to follow,our methods you need to pick up one of our recommended test kits to be ready for opening.

3. ## Re: Proper TC to FC ratio and CYA numbers

Originally Posted by Fearman
Getting ready to close my pool. Just tested by pool installer. TC is 10.0 (I think their test system will not register above 10.0 but I think TC is above 10), FC is 10.0 (but again I think limited by test system), pH is a 7.7, TA is 165, CH is 300, CYA is 135. Reading the TFP Pool School items leads me to believe the TC should be less than .5 while the FC should be about 3.0 and CYA should be about 50. Should I plan on replacing about one half my water come Spring while opening and if I do, will the TC to FC ratio come in line?
Hello and welcome to the forum!

If you refer to the Chlorine/CYA chart from pool school you will see that with a CYA of 50ppm, your minimum FC level is 4ppm, with a target of 6ppm. I'm not sure where you would have seen a FC of 3ppm recommended for a CYA of 50ppm on this site.

If your CYA is indeed 135ppm (standard CYA tests top-out around 90-100ppm), a FC of 10ppm is the lowest it should ever be, with your target FC at around 15ppm.

If this were my pool, I would replace 60-70% of the water to get to a CYA around 40-50ppm which should be fine for your location.

If you are using chlorine tablets in the chlorinator listed in your signature that is the root of your high CYA issue. For every 10ppm of chlorine you get from a tablet, you are also adding 6ppm of CYA. While the FC will be used up by bather waste and other organics, the CYA will not, and will continue to accumulate as long as you use tablets and/or powdered dichlor (shock/super shock, etc), which is actually worse.

What are your goals for next year's pool season?

Dom

4. ## Re: Proper TC to FC ratio and CYA numbers

Thanks for the input. Youa re correct that I mistakenly substituted TC for CC. I've been told by pool "pros" around here that the FC and CC numbers neeed to be the same - that the only thing to worry about is when the CC number is large and the FC number is zero or very small. From what I know, when the CYA is high, the amount of FC needed to sanitize is greater than when tthe CYA number is "in range". So an FC to CC ratio of 10 to 10 with a CYA number of 135 is not as good as a ratio of 3 to 3 for example with a CYA nuumber of 40. Does this comporrt with your thinking and understanding?

5. ## Re: Proper TC to FC ratio and CYA numbers

Well, that has SOME degree of correctness but not very much.

I suggest you read "The ABC's of Pool Water Chemistry" up in Pool School. That should give you the correct foundation that will start to build your pool knowledge and should lead you to ask a lot of questions. We'll help.

6. ## Re: Proper TC to FC ratio and CYA numbers

Originally Posted by Fearman
Thanks for the input. Youa re correct that I mistakenly substituted TC for CC. I've been told by pool "pros" around here that the FC and CC numbers neeed to be the same - that the only thing to worry about is when the CC number is large and the FC number is zero or very small. From what I know, when the CYA is high, the amount of FC needed to sanitize is greater than when tthe CYA number is "in range". So an FC to CC ratio of 10 to 10 with a CYA number of 135 is not as good as a ratio of 3 to 3 for example with a CYA nuumber of 40. Does this comporrt with your thinking and understanding?
There is no FC to CC ratio. I think you are still confusing CC with TC. If FC & TC are always the same, that would net a CC of 0.0ppm as TC=FC+CC.

Again, there is no FC to CC (or TC) ratio. The ratio that matters is FC to CYA.

Ideally, your CC should be 0.0ppm.

Now, in the real world there will be some CC's at times, especially with a pool that is being used often, but in a well maintained pool they are usually 0.5ppm or less.

I advise you take Dave's advice and spend some time reading the articles in Pool School, it is your gateway to a beautiful, inviting & Trouble Free Pool.

Dom

7. ## Re: Proper TC to FC ratio and CYA numbers

I was and still am in same situation with my CYA. I knew nothing about what hardener really is(its actually CYA) until my chlorine was over 5 and was still getting some algae on walls. Went to pool store and they told me my CYA was really high and I had to drain and refill I never heard that. Searched and came across this site and did some research. Here's the skinny from someone that just went through this. Your 3" tri-clor tabs have a ingredient called cyanuric acid or CYA or sometimes called hardener(on test strips). CYA is actually needed in outdoor pools as UV rays will reduce your chlorine by 90% in 2 hours! You need approx. 30-50 PPM of CYA in a vinyl pool to counter this effect. All tabs and most shock add this and after a while it gets too high and you need to maintain a very high chlorine level because the CYA binds to the active bacteria and algae killing chlorine and really makes it somewhat ineffective at lower doses. You need to keep a 7.5% ratio of FC(free chlorine) to CYA. For your 135 CYA in a vinyl pool you should have a FC of a minimum or 10 to 17 max to effectively kill algae. In my case I am at 160 and needed to be at FC 15 that's why I had a issue. The only cure for this is dilution of the water by draining and refilling CYA never really goes down on its own.

Its a vicious circle that the folks here love to help with. The more pucks you use the higher your CYA goes and the higher your chlorine needs to be so more pucks. Then you have a algae issue so its off to the pool store to spend a couple hundred to clean it up. The only thing you need to do is get a good test kit that has the FAS-DPD test so you can measure accurately and keep you FC as to what is recommended by your CYA levels until you can reduce it. I will be doing that after the winter. use the pool math calculator to input your pool size and CYA and current FC that you measured from your new test kit and it will tell you how much bleach to put in. my wife picks up a couple of 121oz "great value" 8.5 % bleach at walmart for \$2.96 usually use about 1 1/2 jugs a week. Been doing this for about a months its a little bit more hassle than the automated pucks but cheaper. Eventually we need to get the CYA back to 30-50. Also as a FYI after you do your FC test, you check for CC. Typically should be 0-0.5 any more you probably have algae getting ready to bloom and make it cloudy. or worse green.

8. ## Re: Proper TC to FC ratio and CYA numbers

Originally Posted by miwitte
I was and still am in same situation with my CYA. I knew nothing about what hardener really is(its actually CYA) until my chlorine was over 5 and was still getting some algae on walls. Went to pool store and they told me my CYA was really high and I had to drain and refill I never heard that. Searched and came across this site and did some research. Here's the skinny from someone that just went through this. Your 3" tri-clor tabs have a ingredient called cyanuric acid or CYA or sometimes called hardener(on test strips). CYA is actually needed in outdoor pools as UV rays will reduce your chlorine by 90% in 2 hours! You need approx. 30-50 PPM of CYA in a vinyl pool to counter this effect. All tabs and most shock add this and after a while it gets too high and you need to maintain a very high chlorine level because the CYA binds to the active bacteria and algae killing chlorine and really makes it somewhat ineffective at lower doses. You need to keep a 7.5% ratio of FC(free chlorine) to CYA. For your 135 CYA in a vinyl pool you should have a FC of a minimum or 10 to 17 max to effectively kill algae. In my case I am at 160 and needed to be at FC 15 that's why I had a issue. The only cure for this is dilution of the water by draining and refilling CYA never really goes down on its own.

Its a vicious circle that the folks here love to help with. The more pucks you use the higher your CYA goes and the higher your chlorine needs to be so more pucks. Then you have a algae issue so its off to the pool store to spend a couple hundred to clean it up. The only thing you need to do is get a good test kit that has the FAS-DPD test so you can measure accurately and keep you FC as to what is recommended by your CYA levels until you can reduce it. I will be doing that after the winter. use the pool math calculator to input your pool size and CYA and current FC that you measured from your new test kit and it will tell you how much bleach to put in. my wife picks up a couple of 121oz "great value" 8.5 % bleach at walmart for \$2.96 usually use about 1 1/2 jugs a week. Been doing this for about a months its a little bit more hassle than the automated pucks but cheaper. Eventually we need to get the CYA back to 30-50. Also as a FYI after you do your FC test, you check for CC. Typically should be 0-0.5 any more you probably have algae getting ready to bloom and make it cloudy. or worse green.
There are a lot half truths and downright mis-information here.

The most important thing is 7.5% FC to CYA is the maintenance dose of chlorine, meaning the minimumum you should have to keep algae away. Once you have algae you need much higher amounts of chlorine to kill the active bloom.

9. ## Re: Proper TC to FC ratio and CYA numbers

CYA is not an ingredient in Trichlor tabs. It's part of the actual chemical makeup of Trichlor. This is why for every 10 ppm FC added by Trichlor, it also increases CYA by 6 ppm. And why for every 10 ppm FC added by Dichlor it also increases CYA by 9 ppm. These facts are independent of concentration of product or of pool size.

10. ## Re: Proper TC to FC ratio and CYA numbers

Also, I believe you are mistaking hardener for CYA. 'Hardener' is what you add to raise your calcium hardness number, not your CYA number.

11. ## Re: Proper TC to FC ratio and CYA numbers

CYA is often called Sunscreen. I have never heard it called hardener. "Hardener" is normally a part of a two pack filler for eg bogging up rust holes or dents in cars or fibreglass.

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