Pool Balanced but still have Green Algae

[momtaps]

I tested the pool on Friday - everything was all in balance. Why do I still get green algae on the north facing wall of my pool? I've cleaned my cartridge filter twice this month hoping that would help. I keep it brushed off as soon as I see it. I have natural rock that touches the water on that side of the pool. Could there be some sort of algae that is seeping out of the rocks? The green starts at the surface of the water then grows downward. Water is crystal clear and beautiful. I'm using the last of my tri-clor tablets then going to the bleach method.

FC 2
TC 2
CC 0
TA 130
ph 7.8
CYA 35
CH 420

Thanks!

 

[gboulton]

To my inexperienced eye, I'd wager it's because you don't have enough chlorine to kill off existing algae.

I suggest:

Shock the pool according to the directions here.

I'd also advise a higher post-shock FC level, in the 4-5 range, as suggested here.

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By all means, chime in experts if I've missed anything, or misled the OP!

 

[Bama Rambler]

It's definitely because you don't have enough chlorine.

Is it growing on the shady side of the pool? If so it's probably mustard algae. :-(
Is that an area of poor circulation?

Have you ran an OCLT (see sig if you don't know what that is)?

 

[maxepr1]

I would question your test kit. If you have visible algae you have to have some CC? You shouldn't be able to pass a OCLT.

 

[JohnT]

If you have visible algae you have to have some CC? .

Not in my experience. I never see CC from algae.

 

[momtaps]

The instructions for shocking the pool says to add some chlorine until you reach the shock level (which according to the chart I am aiming for a 16). How much is "some?" Should I start with 1 gallon, 5 gallons? etc. I tried to use the pool calculator - entered the current FC at 2 and goal at 16, but when I hit the calculate button, nothing happens. I have searched the board looking for this answer but can't find a clue as to how much to start with. Help!
My test kit is the leslies total poolcare DPD Test Kit. They didn't have the recommended one. I need to order it.
Thanks!

 

[JasonLion]

4 1/2 gallons of regular 6% bleach to raise FC from 2 to 16 in 17,000 gallons. Remember that none of the common jugs are exactly a gallon.

 

[momtaps]

Thank you! How did you figure that out?

 

[Smykowski]

Thank you! How did you figure that out?

Did you put your pool size in before you started?

 

[momtaps]

I had entered 17,000. When I removed the comma - 17000, it worked. Thanks so much for everyone's help.

 

[momtaps]

OK, I got my new test kit TF100 in the mail today and began the process of shocking my pool. According to the pool calculator, with today's test results, I needed to add 2.1 jugs of bleach to raise the FC from 5 to 16. I did this, waited an hour, and tested again. I am at 20.5 now! Is that OK? I am shocking because of algae.

CYA 40
FC 5 (before shocking with chlorox 6%)
CC 0
TC 5
TA 80
ph 7.5

 

[linen]

OK, I got my new test kit TF100 in the mail today

According to the pool calculator, with today's test results, I needed to add 2.1 jugs of bleach to raise the FC from 5 to 16. I did this, waited an hour, and tested again. I am at 20.5 now! Is that OK?

That is fine. How sure are you of your pool volume?

CYA 40
FC 5 (before shocking with chlorox 6%)
CC 0
TC 5
TA 80
ph 7.5

The rest of you numbers look good! Have you measured CH yet?

 

[momtaps]

Just tested the ch - 3 times with 3 different results!

Leslies kit - 410
TF100 - 800 1st time, 650 2nd time

What's up with that?

 

[Bama Rambler]

Are you using a speedstir? If not I'm not surprised at the variance. The CH test is very hard to do repeatedly by hand swirling.