CYA Through the roof?

I am a new user to this forum and I am very hopeful I will finally begin to get a handle on taking care of my pool. I started to prepare my pool for summer about a month ago and as is typical it was green. I shocked it, cleaned it, etc but it just would not clear up no matter how much I shocked it. After finding this forum, I got a good test kit and when I measured the CYA it was basically off the scale. My test kit measures by mixing a reagent and then dropping the solution into a vial with a black dot at the bottom and when you can't see the dot you look at the scale to determine the ppm. The scale starts at the top and reaches 100ppm at about half way down. I couldn't see the dot at about 1/4 full (half way to 100), and looking at the scale, it is not a linear scale so I don't really know where my CYA is. What I can't figure out is where it came from. I have not added CYA and I refilled the pool completely the beginning of last year. I have only used regular chlorine tablets and shock since refilling as well as pH+ a couple of times. Here are the results of my tests:

TC = 4 (top of scale)
TA = 90
pH = 6.8
CYA = >100

The pool is 18,300 gal

Any assistance would be appreciated although I am pretty sure at this point the answer is going to be "Drain it and start over!"

If it were my pool, I would drain half the water and that would take the cya to 50 which would be a good number. The other comment I have is that ph of 6.8 is too low. And, since on most testkits, 6.8 is the lowest reading it will show, it may actually be much lower. Any reading below 7.0 is acidic and will damage your pool. Get some Borax in there and raise it up to around 7.4-7.6. Welcome to the forum. Let us know if we can help more. We're here!

Edit to add- Have you used trichlor tablets as your source of chlorine? If so, that is where your cya came from. Those tabs are stabilized which means they have cyanuric acid in them. Also, upon rereading your post more carefully, I see where you say you don't really know what your cya reading is. So, draining half may or may not take it to 50. You may need to do a couple of partial drains if the first one doesn't take the cya low enough. Do NOT, however, drain your whole pool at once or you risk floating it out of the ground or ruining a liner if it is a liner pool. The other option is to keep the high cya and just run higher than normal chlorine readings. But, like I said, if it was my pool, I'd do some partial drains and get that cya number down. Hope this helps.

Thank you for responding so quickly. Since I don't really know how high the CYA is, should I only drain it half way and check it after refilling? What I don't want to do is find out it is still too high and have to drain partially and refill again. Any idea how it could have gotten so high or could anything else cause this result to be incorrect?

Unfortunately, if your cya is well over 100 as it may be, it may take more than one partial drain/refill to get the cya down. If the cya really is 100, then draining half-way and refilling will take it down to 50. But, if your cya is really much higher than that, draining half and refilling will only reduce it by half. Even though it may still be higher than you really want it, one time draining half and refilling may at least get you down to a more manageable level. Go ahead and drain half, refill and then retest cya and let us know what it is and we'll advise you from there.

Your question -- how did the cya get so high? What have you been using to chlorinate with? You say "regular chlorine tabs and shock" which is most likely trichlor tabs and dichlor powder, both of which have cya in them. Actually, your scenario is a pretty typical problem that unsuspecting pool owners have. They use these products over a long period of time and don't realize that in addition to adding chlorine, they are also adding cya. Over time, the cya level builds up really high and as a result, the "normal" chlorine level that always worked before to keep their pool algae-free no longer will work. Higher cya levels require higher chlorine levels. And, that is the part that most pool owners don't know. I'm suspecting that is why you can't get your pool clear this spring even though you say you have shocked it to no avail.

I know it is a pain to do, but you really do need to drain half (maybe even two-thirds but no more than that at once) and then refilll and retest and we'll help you go from there. Also, look at the ingredients on the tabs and shock you have been using and let us know what they are. Like I said, probably trichlor and dichlor.

Let us know how it is going!

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Originally Posted by swilson

Thank you for responding so quickly. Since I don't really know how high the CYA is, should I only drain it half way and check it after refilling? What I don't want to do is find out it is still too high and have to drain partially and refill again. Any idea how it could have gotten so high or could anything else cause this result to be incorrect?

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Watermom has deciphered the most likely cause. You can always repeat the CYA test but if you've been using TriChlor or DiChlor tablets or shock powder, this is the culprit. CYA can build up very quickly (a matter of a few months) when using chlorine compounds such as Trichlor. You can also try diluting the pool water sample with tap water (50:50) on your second test and double the result. Either way, reducing the CYA by draining some pool water will make it much easier to manage the pool chemistry.

I notice also that you didn't state the Calcium Hardness (CH) level. If your pool shell is composed of concrete/plaster or tile you might want to consider changing your chlorine source to Cal-Hypo -- but you must monitor CH level so the calcium doesn't get too high (> 400 ppm). My pool setup uses a Salt Water Chlorine Generator (SWG) cell to santitize but if I didn't have one I would use straight 6% bleach or 12% liquid chlorine. No additives and no worries about too much CYA or calcium.

Just to add a comment, the trichlor is also what's keeping your pH down to the point that you have to add pH ++--by partial drain and refilling, assuming your fill water has a higher pH than that, you'll be correcting that problem at the same time.

I would highly recommend that you stop using trichlor tabs and dichlor shock for the time being, and switch to something else that will not continue to drive your pH down and your CYA up....most of us use plain, unscented bleach that does not add any unwanted chemicals to your pool--it breaks down into chlorine and salt, which is actually good for your water.

Or you might want to consider a salt water generator--I'm looking at adding one to my pool this year because it will make your pool almost as maintenance-free as it can get!

By the way, welcome to the forum!!

Janet

First I want to thank everyone for the replies. I did check and I have been using trichlor so I guess that identifies the culprit. I have actually decided to use the BBB method once I get this cleared up. When I went and bought the test kit I also bought bleach, borax and baking soda in bulk. I am draining the pool to one-thirds to one-half and refilling and then I will test and consult the pool calculator to see what I need to add. I will let everyone know how it progresses.

Good. Keep us posted. And .... then -- no more trichlor. Trichlor does have its place in pool care. If it is a fresh fill where you know there is no cya, you can use trichlor to add chlorine and cya at the same time, but you have to monitor the cya level as it builds up. Once you hit somewhere between 30-50 cya (I like around 40), you have to discontinue the trichlor.

Did you look at the ingredients of your 'shock'?

Swilson, what is your water supply? Reason I ask is if it is city water you may have a bill through the roof. You may want to consider using a large plastic sheet instead of just draining-refilling-circulating etc. You can get a large plastic sheet and lay that on the pool. Fill on one side and drain off the other. The membrane keeps the new and old water separated and theoretically you can do a complete exchange without dropping the water level and risking damage to the liner if that's what you have. Sounds like you have a relatively large pool so I don't know if you would have to stick a couple sheets together to get the size. How you would do that I'm not sure. Duct tape may work for a while but maybe there is some kind of adhesive or solvent that would work and hold for the time needed.
Just some thoughts that have been proposed before.
Al

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Originally Posted by swilson

When I went and bought the test kit I also bought bleach, borax and baking soda in bulk.

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Just so you know, BBB does not mean you will normally need to use bleach, borax and baking soda. It is more of a philosophy about testing your water with an accurate test kit so you really know what is in it and then making appropriate adjustments adding only what is really needed, often using less-expensive grocery store equivalents to pool store chemicals. It is a "less is more" philosophy that generally avoids the need for any algaecide, phosphate remover, clarifiers, flocculants, enzymes, regular shocking, etc. It is a program based on careful observation and sound scientific principles rather than marketing hype.

So, in practice, you will be using mostly bleach or chlorinating liquid (whichever is less expensive or more convenient for you) and will not need to use baking soda (to raise TA) very much and may not ever need to use borax (to raise pH) unless you were to use your Trichlor tabs again, say while on a short vacation. It is more likely that you will sometimes use Muriatic Acid to lower the pH. In my own 16,000 gallon pool (shown here and here), I only add 12.5% chlorinating liquid around twice a week (I have a mostly opaque electric safety cover so my chlorine usage is a little less than 1 ppm FC per day) and add a small amount of acid every month or two. That's it -- around $15 per month in chemical costs during the 7-month swim season.

Richard

OK, drained about 2/3 of the pool and filled with city water. Here are the test results:

CYA = 80-90
TC = .5
pH = 7.5
TA = 110
TH = 320

So, based on the pool calculator, it looks like all I need to do at this point is add bleach to get the chlorine level up. Should I only get it to the recommended level of about 4 or should I shock initially. My bleach jugs are 182 oz and the calculator indicates I should add about 1 jug to get it to about 5.5 and 2 jugs to get it to 10.

Wow, if a 2/3 drain resulted in CYA of 80 or 90, then it really was through the roof--no wonder you're having trouble getting it clear!!!
Is your water still green? If it's at all green or cloudy, then you need to shock it by adding enough chlorine to get to 20 ppm. You need to maintain that 20 ppm until it clears, then when you allow it to drop back down, keep it between 5 and 10 ppm--if you go below 5 ppm, you're going to have a really hard time keeping it clear. I know this sounds like a whole lot of chlorine, but that's unfortunately what happens when you have an overstabilized pool, and that's why in MOST cases, CYA of 40 or so is recommended. The good news is that with the stabilizer that high, it will be a longer time in between chlorine additions since the chlorine level won't drop as fast.

Janet

Still working on it but it looks like some progress is being made. Quick question, since I need to keep the chlorine level around 20 till it clears, what it the best way to test that, my kits only go to 5?

You can dilute your pool water sample with distilled water (tap water usually has chlorine or chloramine in it) and then multiply your result by your dilution amount. So if you dilute 1:1 with equal parts of each, then multiply your result by 2. If you dilute 1 part pool water with 2 parts tap water, multiply the result by 3.

You should definitely get a good test kit. You can get a Taylor K-2006 test kit at a good online price here (the "C" version you refer to is larger in size so is more expensive, but you can get that for a better price here) or the TF-100 you can get here with the latter kit having more volume of reagents so is more comparably priced per test. A comparison of these two kits is in this post. These test kits use a FAS-DPD chlorine test that can measure up to 50 ppm FC, can measure Free Chlorine (FC) and Combined Chlorine (CC) separately and accurately, and can be as accurate as 0.2 ppm when using a 25 ml sample (when shocking, you usually use a 10 ml sample for 0.5 ppm accuracy).

Will it be accurate if I just double the sample from the pool and multiply the reading by 2, or triple the sample and multiply by 3, etc?

No, if you double the sample from the pool, then you actually have to divide your result by 2 instead of multiplying.

The sample from the pool should be diluted 1:1 or 1:2 with water that doesn't contain chlorine for the test to work--and even then you're going to lose some accuracy with each dilution...

Janet