Algae problems

[Marcussen]

I have a 24 foot round AG vinyl pool. It was doing OK untill I went on vacation for two weeks.
When I returned it was black/green.
I tried algacide and shock. but the algea is just returning.

Then I found this board and tested my pool.

Day one
CL 0
PH 7.8
CYA 0

I went to the store and bought some bleach and stabilizer.
Added 3.5 gallons 6% bleach and 3 lbs stabilizer

Day 2
CL 1
PH 7.8
CYA 40
Pool is still green.
Added 3 gallons 6% bleach
I also bought a new 6 way test kit (previous was test strips)

Day 3 (today)
CL 1
PH 7.8
CYA 30
Alkalinity 300
Hardness 500
the pool is still green.

Where is the clorine going?
Daytime temp 105ºF the pool is in full sun.
Also have several trees loosing leaves due to the dry weather but they are removed daily.
Any suggestions?

[aylad]

The chlorine is being used up by the algae in the water. In order to clear the pool, with a CYA of 30, you need to shock the pool to 15 ppm and HOLD IT THERE by testing and re-adding enough to get back up to 15 at least 2-3 times daily. The chlorine needs to be high and stay high in order to kill the algae. This will take quite a lot of bleach at first, but as the algae starts to die you'll start seeing the chlorine consumption come down. Brush your pool daily, keep removing the leaves, and keep your filter on 24/7, backwashing as needed, and the pool will clear up.

Janet

[Sherra]

Daytime temp 105ºF the pool is in full sun.

That, plus the fact that you're fighting algae is where your chlorine is going. Get your chlorine level up to 15 as per Ben's Best Guess Chart, and keep it there (test and add chlorine as needed 2-3 times per day) until your chlorine level holds overnight. Then let it drift down to between 3-6 ppm and keep it there. Again, per Ben's Best Guess Chart. It's very common to loose around 3 ppm during the day even with the best maintained pools when they are in full sun and that high of an air temp. But, since you're fighting the algae you need to keep it at shock levels until it "holds" over night (losing no more than 1 or 2 ppm over night).

Edited to add: Posting the same time as Janet.