It appears that I have lost my CYA. Was it was the extreme heat and bright sun? Where did it go? It was just over 60 a couple of weeks ago, and yesterday evening it barely even registered on the two tests I ran. I could still vaguely see the black dot when the tube was completely full. I first used the solution I had in my old kit and didn't think the result could possibly be accurate so I tested again with the new refill solution I recently purchased from TFTestkits and got the exact same result. I have topped the pool off a couple of times due to evaporation but I certainly haven't replaced enough water to lose almost ALL of my CYA. I was afraid to add any more last night because I thought maybe something was causing my test to results to read wrong. I certainly don't want to overshoot it like it did early in the season. I'm totally confused! Please share your thoughts and/or explanations. My water temp is 82F if it makes any difference. All of my other numbers are good.

Just taking a stab in the dark, how old is the cyanuric acid you were using?
I've been told it has a long shelf life but perhaps you've exceeded that???

What type of light are you doing the testing in. And are you sure the first test you ran earlier when it was 60 was accurate?
Are you letting the mixture sit long enough? (Shake about 30 sec; let stand 2-3 minutes; briefly shake again.)

You may want to try it again in indirect light. Make sure tube is waist high, add some mixture to the tube, let the water settle and your eyes adjust, then continue/repeat.
When done, dump the water back into the test dropper and do it a couple more times.

Cramar, I purchased the CYA in the spring at a pool store that gets tons of business. I don't think it's too old.

WSP, I test pretty much exactly as you described, and I do it outside in indirect sunlight. I'm sure the old test reading of 60 was correct. I've been testing often and impatiently waiting for it to fall back down from over 80, where it was this spring. I never meant for it to get that high. My daughter thought she was "helping" me by adding more when she saw that the sock was empty while I was at work. This happened a couple of times before I found out she was doing it.

Saw this posted elsewhere, is it relevant to your situation:

CYA can get converted to ammonia by bacteria if you let the Free Chlorine (FC) level get to zero, but this is neither reliable nor predictable. If this occurs, it can take a LOT of chlorine to get rid of the ammonia.

You mentioned your daughter adding CYA, since she is involved in the maintenance process any chance she added a bunch of water? Any chance she removed too much during a back wash and simply replaced it so no one would know?

Yea, something is amiss here, and I don't think it's the testing. Boy, if she did backwash too long...it would have been WAY too long. Possible I suppose...mmboy, Im interested in this one now. Do keep us posted...very curious now.

It can and does happen tho we do not hear of it too often. And it sure does take a lot of bleach/chlorine to get rid of it.

Samantha, we could get a better clue to what is going on if you post a full set of test results.

Is there a way some fertilizer could have gotten into the pool?

I know it didn't happen by backwashing because we have a cartridge filter... backwashing isn't even an option on it. My daughter is not really involved in the pool maintenance. She hasn't touched it (except for swimming in it) since I chewed her out for adding the CYA without asking first. Taking care of the pool is solely on me. I test it and add bleach every night myself. I'm positive my FC has not been below the minimum recommended level of 5. I have been bumping it up to about 10 - 12 ppm every night because of the 100 degree weather we've been having. This really is confusing.

I agree with Butterfly...It would help us if you post your test results!

....and what about the fertilizer question?

I'm watching this thread closely, as mine also dropped from a solid 80 to 45 a couple weeks ago. Not hijacking or asking questions yet, but it is puzzling.

Sorry I didn't post back last night, I had a migraine. I went straight to bed when I got home from work.

I don't see how any fertilizer could have gotten into the pool. We haven't used any, and we don't have any crops growing near us. I tested and added bleach this morning before leaving for work. I normally wouldn't have my FC this high, but we have a good chance of getting thunderstorms today. I upped it some to be on the safe side.

FC: 9.0
cc: 0
pH: 7.6
TA: 100
CH: 70

I'm not sure if it makes any difference, but I did use some Roundup around our yard last week. I really don't believe any of it could have gotten into the pool. Everything I sprayed was 100' or so away from it and the wind was not blowing at all that day. Man was it HOT that evening!

ultra800_96, feel free to jump in and add whatever you want or ask questions. Maybe between all of us we can figure this out. It is definitely puzzling.

I've been reading a lot of other posts from the past with similar issues. Most of them just mentioned adding some more CYA and see if it holds. One did mention the ammonia thing that was mentioned earlier in this thread, but there was no real definitive answer.

I would run one more CYA test today and see where it's at.

I had brought mine up to 80 in a couple different increments due to installing a SWG this year. I started with fresh refill testing regents I purchased from TFtestkits, stored in a closet in my home. A friend had stopped over & was present when testing the 80 figure, we both did the test independently with multiple pour-backs to verify the 80 level. It came out everytime with us both to be a solid 80. Perfectly clear, sparkling water & two weeks later I tested again. Again multiple tests, under 50 (I guestimated 45) every time. I had just enough HTH stabilizer (purchased from Wally World this spring) to get me back to 60 per the pool calculator. I waited a week, sure enough it was back to 60 after multiple tests. No fertilizer, roundup, or algae bloom during that time. The only thing that might have been a factor, is in a nightly testing with the chlorine/ph test block, one time during the period I came up with a 1 fc. I checked the cell, everything was fine, water was still very clear with no signs of algea, dumped in one 182 oz jug of 6% to put me back up to around 8, the SWG since has had no trouble maintaining a 5 ish FC level & previously had no trouble before. No extreme chlorine demand after the incident, so I can't see the ammonia conversion happening. Everything's been fine since, but for kicks I'm going to do another test tonight to see if the 60 is holding. Your thread just caught my eye, because this is what I experienced. No catastrophe for me, but very puzzling.

ultra,

Had a lot of rain? Heavy use from kids splashing water out? That's all I can think of.

I would add that mine has gone from 50ppm in April to just under 40ppm yesterday but that's pretty easily attributable to splashout and rain/refill.

Samantha,

Measure your FC any given morning very early and then measure it again that evening. If you lose the majority of your FC, you can safely assume you have no CYA and replenish it.

I have no explanation as to why it disappeared. The ammonia conversion is not valid for your situation.

Dave,
Maybe 1-2 inches of rain. My pool doesn't get used heavily, so not alot of splashout. I can't quite totally remember, but I don't think I ever backwashed/wasted during that period. It was very hot, we did have a couple thunderstorms & I did have some evaporation. Ive had your testkit for 3 seasons now, & I love it. The cya test is subjective, I know, but this year, especially going to a higher level, I've felt more confident in the results of most tests, especially since adding the Speedstir. The only test yet that I have trouble reading is the CH test. It turns blue & I can't seem to read when it ends turning. Probably bad eyesight & should video the test & playback, lol. Anyway, not to hijack, or to get off topic. Thanks for your reply.

I had the same problem just a few weeks ago. I get how splash out will take out cya but not how evaporation would affect the cya since it doesn't evaporate?