Persistent Green Algae

Aug 30, 2007
Hi - Newby here. This looks like the place. Thanks in advance for your help.

I have a 12k gallon inground pool with vinyl liner, Hayward DE filter.

Got a new test kit (Taylor) before posting. Readings are:

FC - 5ppm+ (5 is the max on my kit)
TC - 5ppm+
AL - 80
PH - 7.2

I have been adding about 8 oz stabilizer per week and about the same algicide. The chlorine
I have been using is in small tabs in the skimmer and dissolves in about a day. I have been
consistently been adding 3 tabs per day. I live in CT and the pool gets direct sun.

I have been running the filter 12 hours per day, changing the DE monthly. Only shocked
the pool when I opened it.

My problem is that I get green algae growth in spots - where the liner has seems and in the
corners mostly. I just brush it off every day or two. The water is very clear. There are flowers
next to the pool which let a fair amount of petals in (organic matter). I use the leaf rake for any
big stuff and brush and vacuum the little stuff weekly,

The questions: Is my chlorine level too high? The algae growth intensifies when I let it go down.
If I shock, do I need to get a better kit to test higher levels of chlorine?

This is my second year of doing my own maintenance. Last year around mid-summer I went away
and the responsible person forgot to add chlorine and I had bad algae growth and shocking cured



TFP Expert
Platinum Supporter
LifeTime Supporter
May 7, 2007
Silver Spring, MD
You probably have way too high a CYA (stabilizer) level. You said you were adding stabilizer weekly and the tabs add stabilizer as well, so it has surely gotten too high by now. The higher the CYA level the more chlorine you need to use. From the sound of things the CYA level has gotten high enough that the amount of chlorine you have been using is no longer sufficient.

You really need to get your CYA level tested. Any pool store can presumably do that for you or you could get a test kit that can test for CYA. It would also be very nice to get a test kit that can test for the high FC levels you are going to need to have given your CYA level.

The only practical way to reduce CYA is to replace water. If your CYA level is as high as I think it is you are probably going to need to do a fair bit of that.


Mod Squad
TFP Expert
Platinum Supporter
LifeTime Supporter
In The Industry
Apr 1, 2007
Sebring, Florida

Just as reinforcement, I was about to post info virtually identical to the advice Jason has provided.