CYA zero? What happened to my reagent?

Mar 10, 2016
San Diego
I refilled my pool last summer, dumped in two full bottles of dichlor from home depot (by my calculations, I have around a 20k gallon pool, via poolmath calculator).

I had issues with my CYA test last year. When testing my dad's pool or my old water CYA was through the roof and it was super cloudy. But last year when refilling the new pool and using the dichlor I couldn't get the dot to disappear at all. Okay, maybe my calculations were wrong so I go and buy the 50 cya from tftestkits and same thing, it's sort of cloudy but I could barely make out the dot on the Taylor kit 2006.

Well, I was in Europe and pump stopped working and had a monster swamp. My pool friend came over and before I could say anything he dump a ton of trichlor in the pool. I wanted to yell stop but who am I, gonna tell a pool guy he doesn't know what he's doing. So I figure, CYA must be through the roof. So I go to test the CYA and it's zero. No cloud. Water is crystal clear. Shook it vigorously. Clear.

I bought my Taylor 2006 kit back in the summer of 2015. I don't think the CYA reagent would go bad that fast? The kit is so old I'm thinking of scrapping it and just getting a new kit. Maybe my Taylor black dot is extra black or something (yes I did the test with the sun behind my back).

Other than the CYA reagent being bad, what else could it be? I doubt the algae ate the CYA, could it? It was a swamp for a week or two.

EDIT: Or can I just buy the reagent refill? I guess I don't need to buy a whole new kit. I'll order that now. What other agents do you think I should replace? It'll be 2 years this summer.
Apr 15, 2016
Central Florida
There is a phenomena that happens to *some* pools that are left at 0.0 FC for extended periods of time where a bacteria gets blown in with dirt and massive amounts of Ammonia are produced as well as CYA being destroyed/converted. This sounds like what happened to you. drain required. It may take several gallons of bleach before it holds a FC for more than a couple hours, but it can be overcome. You can search forums for more info on this, try things like CYA went to zero, lost CYA over winter, bacteria CYA, etc.

Yes, you can order just the CYA chemical, at quite a deal too, $10 plus shipping, on several site but here is what I buy, especially since you still have the mini bottles:
which can refill the little bottles easily (the dropper tip easily pushes/pulls out and goes back in)
or if refilling and storing the big bottle disgusts you:

Also available at some pool stores and/or other websites...but that one is super fresh chemicals and flawless support. Owner is active on this site too.
Mar 10, 2016
San Diego
I'm definitely ordering from TF Test kits. That's just crazy cya can disappear like that. I'll order the kits and manage the algae until then. I definitely don't want to over-CYA my pool.


TFP Expert
LifeTime Supporter
Jun 7, 2011
Midland TX
It's not uncommon actually. The most likely scneario believed to cause it is the consumption of it by Bacteria where it's converted to ammonia. Most commonly it happens in pools that go green, but not always. Not a big deal though, it can be easily replaced.


Bronze Supporter
LifeTime Supporter
TFP Guide
Jun 3, 2015
Don't add any CYA until you confirm what is going on. If you suspect ammonia you can pick up an ammonia test kit, they are commonly used for fish tanks.

To battle the ammonia:

Treatment for Ammonia:
1. Dose FC up to 10ppm. Do not add additional CYA at this point.
2. Retest FC at 10-minute intervals.
a. If FC loss is greater than 50% (5ppm), add FC to bring back up to SLAM level (10ppm) and continue retesting FC @ 10-minute intervals, repeating step 2..
b. Once FC loss is less than 50% (5ppm) you have beaten the ammonia and can begin a standard SLAM.

Add enough CYA to bring level up to 30 ppm and SLAM at FC 12ppm.
Mar 10, 2016
San Diego
Just an update. Didn't have to do any of that, but my CYA was definitely zero. I have brought it up to 30. Mustard algae has returned and plan to slam at 18ppm+ FC. I've waited this long because I have to remove the two light niches and:

1 it's been cold and I didn't want to get in
2 had to figure out some GFCI issues but an electrician took care of that.

Next up after a successful mustard slam (hopefully) is going to 50 or 60 CYA, a stenner and will keep the FC constant (hopefully). Thank you everyone!
Apr 15, 2016
Central Florida
Sounds like you're on a great path, a few reminders/clarifications:
1. PH to 7.2 before sending FC above 10 to 12 for regular SLAM portion
2. Verify CYA 30
3. SLAM @ FC12 (if cya 30) (brush brush brush, pump 24/7 etc)
4. meet three SLAM criteria, then do 24 hour mustard slam at 18.2~19
5. remember, the SLAM cannot fail when done correctly, though there are sometimes surprises along the way
Mar 10, 2016
San Diego
Yeah I'm terrified of the slam. Seen some mustard algae problems (yes it's definitely mustard) so I am going to be as diligent as I can. I took my vacuum inlets that are yellowed stain and dropped them right into a 50/50 bleach solution for a day (okay maybe 25/75) and it's still yellow. I'll probably replace the darn things to be sure.

Can you swim at mustard algae levels?


Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
Houston, Texas
No, but you don't raise the pool to mustard algae levels until the initial slam is completed by meeting all 3 slam completion criteria, then you hold mustard algae slam level for 24 hours. You can swim during a regular slam.