Please bear with me as this is my first post. I am a new pool owner (Missouri) : 35,000 gal inground, vinyl pool with sand filter. Regular use of Trichlor tabs with frequent Dichlor shocking was recommended by other pool owners and the pool store pros. This is common practice here with little regard for CYA levels. After opening and initially cleaning the pool May 19, the CYA level was 26 (pool store reading). By June 20, CYA was 59. I use a Taylor K-2006 kit. By July 4 it was 72. I terminated shocking with Dichlor. On August 7, CYA rose to 95 and I terminated adding any more Trichlor and switched to daily use of bleach keeping free chlorine levels between 2-3 (half to one gallon daily). In the 3-week period between August 7-28, rains have keep the pool level about normal with little splashout and two backwashes. I anticipated the CYA level on August 28 to be 95 or maybe a little lower, but it rose to 120. I'm wondering if the test kit or the tester failed although I tested twice. Being new to pool management, I wasn't even aware of the FC to CYA relationship until well after dosing with Trichlor and Dichlor. I plan to continue with bleach the remainder of this season, but I don't feel comfortable with heavy doses to maintain around 10% the CYA level. The pool water has looked crystal clear all season. Weekday use has only been a couple people, while maybe up to 10 swimmers on the weekends. Our season is almost over and I will need to drain some water at closing and probably a few times before opening again next May depending on snow and rainfall. I anticipate using bleach next year to avoid adding any more CYA unless it's needed. Here are the current water values: FC-2.5, CC-0, pH-7.8, TA-105, CH-100, CYA-120. Any ideas why CYA continues to rise would be appreciated and whether I can get by this year without a major exchange of water until I can reevaluate next spring. Thanks!

The CYA test is accurate to at best +/- 15 ppm below 100 ppm, and 30 above that. 95 vs. 120 is therefore within range for testing uncertainty and doesn't necessarily indicate that the level actually increased. Since CYA only gets in the water from explicit additions in one form or another, I would therefore conclude that the level is in fact stable, treat it as ~110 (which IS going to require a lot of bleach - skimping on that will cause problems), and leave it at that for the rest of the year. Then see where it is in the spring.

If you look at the view tube you'll notice that's the numbers get closer together the closer to 100 you get. so the difference between 100 and 120 isn't very much. It most likely stayed the same the test just isn't very precise.

I would keep adding bleach and wait till next year to see where the CYA is and go from there. A lot of people lose a good bit of their CYA over the winter.

BTW, with FC=2.5 you're begging for a massive algae bloom. You might get lucky and not have one. Or you might not be so lucky. Keeping that at the recommended level for your CYA is the safest approach, though it won't be convenient with levels that high.

Bama Rambler, I noticed the OCLT in your reply and decided to try it. Yesterday morning the FC was 2.5 and I added an half gallon of bleach around 8 AM. It was mostly a cloudy day with some sun in the afternoon. At 8 PM the FC was between 2.5-3. The following morning at 7 AM it was 2.5, no CC, and the water was crystal clear. I assume that means there aren't a lot of organics and critters using up free chlorine. I wonder if what appears to be low chlorine demand is really saving me from big problems like a massive algae bloom. As I mentioned before, our pool gets relatively low use, we have had few large rains this summer, and it takes a tornado to get a lot of debris (leaves, etc.) into the pool. I'll be taking action to reduce CYA levels to at least half what they are now. Thanks again for your input.

I do not trust OCLT at that low a level. There are many instances on this board where people pass at very low FC levels like you have but not at higher levels. So if I was you, I would raise up to your shock level today and redo the OCLT just in case.

With that said, if you pass the OCLT, and since you pool looks clear, I agree to hang on until next year to lower CYA. I would however maintain a higher FC level...CYA actually holds some of your FC in reserve (as chlorimides), so there is no safety issue with the higher (assuming normal FC levels for you CYA level).

Warning, what comes next came from the http://www.troublefreepool.com/pool-water-chemistry-t628.html deep end of chemistry that I should probably not be playing in At 100 ppm CYA and ~ 8 ppm FC (as tested) you active "Disinfecting Chlorine" level is only ~0.035 ppm. At 100 ppm CYA and 2.5 ppm FC you active "Disinfecting Chlorine" level is only ~0.01 ppm, much to low to typically keep your pool algae free./deep end

Bottom line, I would not risk low levels at this point in the season!

Maybe assume 100 ppm CYA for now and not let you tested FC level drop below 8 ppm (I used poolcalculator.com).

I agree with Linen. You're probably going to pass the OCLT but I'd run it at a higher FC level just to be sure.

I also agree that you can wait till next year to deal with the high CYA.

Wow, this is scary stuff. I wish I had this knowledge early in the season. But I will make amends and do a better job of CYA management in the future. I know other inground pool owners around here who dose regularly with Trichlor (at least 5 large tabs weekly) and then add a couple pounds of Dichlor weekly "to be safe". Seems like CYA levels in these pools must be through the roof. In the past, they have told me the more stabilizer (I assumed CYA), the better. They have been doing this for years and their pool water is clear with no algae problems, etc.

Where do you live? I think some of us northerners get by since our season is short and we partial drain for winter.

By the way, it is interesting when you dig a little deeper on those you mention "with no algae problems" you start to hear a little more. Like large water replacements at the beginning and/or end of season, and some other very expensive products they have dumped in there pool. Sometimes, you hear..."yeah my pool is always green in the spring", or "I just drain half my pool and refill", etc. Not always, but it is common. The methods promoted on this board ensures that most pool owners (regardless of climate, and other factors) have a safe and trouble free experience with their pool chemistry (oh and affordable). In addition, those people you mention above, when they do have a problem, tend to not be able to handle it themselves, since they have not learned good testing practices (and a good test kit), so they do not know how to fix the problem other than pump some money to the pool stores. You can search these forums and find scores of people who joined and said "my pool has been fine for years" but now....

I live in Missouri, so I hope the high CYA levels will come down after winterizing (partial draining) the pool and removing water in late fall and early spring from rains. At that point, I will keep it at a manageable level and use bleach as my primary or sole chlorine source. And you may be right that neighbors and other pool owners have been resorting to drastic measures that I may not be aware of. I'll need to direct them to TFP. Thanks again for your input.

It does for me.
I think this is the "trouble free" way to maintain.
Some get lucky, some don't tell the whole story...
locally here someone with a pop-up pool used tabs their first year when they set up their pool for the first couple weeks, then used nothing for the rest of the summer..apparently had no problems. The next year the started with new water and chlorinated same as previous year for a couple weeks, a few days after they stopped the tabs it was green, took 3 weeks and a lot of bleach to fix...they got lucky for one summer...
You bet, let us know if you have any more questions!