Attacking the Algae Tub: FC testing question


Jan 19, 2011
Pursuant to my post in January, I am finally trying to remedy the "algae tub". I am SO GRATEFUL for all of the posts that helped me even believe it is MIGHT be possible to make this pool swimmable. I am on day three of the journey, and now I have questions.

As recommended, I purchased the Taylor K2006 testing kit. I did not drain, but the evaporation was enough that there would be a moderate quantity of fresh water in the swamp. I have been testing FC and shocking from 6am-dark every day, brushing and skimming as much as I can see/reach, cleaning the filter about five times a day, running 24/7.

The first day, I found the CYA 30, so I used the pool calculator to shock, shock, shock, every half-hour to hour. It did not seem to maintain a shock, but the FC registered, when the original shock left it at 1.5 after an hour.

Day two: at least the mystery larvae appeared dead, and the pool was a less ominous shade of green (not so bright).
Until the early afternoon, even dumping copious amounts of bleach would quickly register only a moderate FC level (4-6). Eventually, I found myself with only two small bottles of bleach left, so I just tossed what I had in while I waited a few hours for my husband to come home with more. I figured - if it's not shocking, at least there is FC in there, so I shouldn't lose ground in a few hours...

...then, a mysterious thing happened. After a few hours, I tested again to see how far behind I was, and the FC was "off the charts". (I stopped counting drops after 18ppm.) The water was all foamy (which it had been the initial few hours, but only off and on afterwards).

Day three: The same not-so-bright green (not foamy), and the FC still tests "off the charts", and I only put in two bottles of bleach in in past 20 hours (pH 7.8 - I can't get a reading for CC, either).

Is this normal/ explainable? I don't want to stop shocking and lose ground to the algae, but I don't want to waste chemicals, or damage from supershock. (I had bad directions from the pool store when I tried to clean last fall, and it was a very expensive start-over, not to mention the time spent.) This just doesn't seem right - to jump from average to to super-shock without adding bleach.

Thank you in advance for any words of advice!

13k gallon (24ft round AG)
Hayward CC1500 100gpm cartridge
Victorville, CA


Mod Squad
TFP Expert
LifeTime Supporter
Jul 10, 2009
Houston, Texas
Could you please post a current set of test results? We all a have a different interpretation of "off the charts" so it would help us to help you if we have all the numbers to work with. Also how big are the bottles of bleach you are using and what is the strength?

As the algae is killed off, your FC will start to hold longer, and since the green is lighter is color that shows you are making progress.


Jan 19, 2011
The Shocking/Algae pages only mention CYA, PH, FC, and CC.
As of now, my CYA appears to be zero. (I can still see the dot when it is filled.)
PH, I know will be affected by the chlorine, but 7.8.
FC: Higher than 20. (I'm afraid to keep testing b/c I will run out of the chemical.)
I could never get a reliable CC, b/c you have to get the post-FC H2O clear. (It would turn pink after 20 seconds even before putting the CC chemical in, but...) Adding the CC chemical, I could never get it to approach clear.

I would expect the FC to eventually stay elevated, but it doesn't seem possible to go from 4 to 20+ (and sustains for 24 hours) after adding only two 96oz bottles of bleach.


Well-known member
Apr 12, 2010
East KY
If your CYA is really zero, then use the pool calculator to see how much you need to add to get it to 30ppm, then add it and treat the pool as if it has a CYA of 30 when it comes to shocking; it will take a week for the test to register the addition. Can you post a full set of test results? I know you'll use a lot of regent, but it would help a great deal to know those exact numbers. I believe the FC test must be completed for the CC test to work, but other more knowledgable people can help you with that. If you haven't read it I suggest reading turning-your-green-swamp-back-into-a-sparking-oasis-t4147.html.