New member
Aug 11, 2007

I give up!!! I have allowed my chlorine level to drop below the adequate level so of course i ended up with an algae problem. AT first I didnt know that chlorine was uneffective with the alkalinity level too low. So, I corrected that and shocked the Crud out of it. my intilial dose was 10 pounds of shock with no results. I then continued to add 5 pds until I had added 25 pds over a 2 1/2 day period. I have a 26,0000 gal inground pool with vinlye liner. I had no results. I then checked my CYnuric acid level and it was over 100. I then drained the pool to below the second step in the shallow end, about 2 1/2ft . added fresh water, shocked again and still green algae. I then gave up. My alkalinity is 180 which is high normal is about 140. Ph is 8.0 cynuric acid is about 40. What should I do!!! Please help!!


Mod Squad
TFP Expert
Apr 4, 2007
SW Indiana
I've never heard of any relationship between alkalinity and chlorine effectiveness. To control algae, you don't do a one time "shock". You raise your chlorine to your pool's shock level based on your CYA level as given in the chart in "The Stickies", and hold it there until the algae is gone. This will require testing and adding chlorine at least three times a day, preferably much more often that that. A full shock level of chlorine can be gone in just a few hours with algae.


TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
Getting your PH down to 7.2 to 7.4 before shocking will help significantly. Chlorine is much less effective at high PH levels. Keep in mind that the PH tests tend to be a little unreliable with FC between 10 and 15 and totally meaningless with FC above 15.


TFP Expert
LifeTime Supporter
Mar 29, 2007
Coastalish 'down easter'
Hi and welcome here Corinne :goodjob: What powder are you using to shock? From the sound of your experience, it's di-chlor - and if so, you are adding more cya to the water with the chlorine, making the chlorine less effective :shock: CYA is needed to keep the sun from burning off the chlorine, but also 'slows' the chlorine down - as a result, you need a higher ppm of cl as the ppm of cya goes up to do the same job. Liquid bleach does not add cya and therefore is recommended for chlorinating and shocking - please see the "stickies" for further info.