Algae returns at FC level of 7

[DivingIn]

In July while on vacation my chlorine level dropped to 1, and there were light grayish-green patches of algae on the bottom. I SLAMmed and thought the problem was fixed. But since then, if the chlorine drops to 7 or below, the patches re-form. With my CYA at less than 30, I would like to keep the chlorine level at around 4-5, but I can't because of the patches coming back. When I raise the FC level to above 10, the patches disappear.

What kind of algae acts like this? Do I really need to keep my FC above 7 all the time? Maybe I didn't SLAM it long enough?

Right now:
FC: 10
CC: 0
pH: 7.1
TA: 120
CYA: 20

 

[northrn]

If you have visible algae, you need to follow the SLAM process to the letter. In order for a SLAM to be complete, you need crystal clear water, CC < 0.5, and an overnight chlorine loss of < 1 ppm. If you fail any one of the three criteria, the SLAM is not finished. Good luck!

 

[pwrstrk]

I'm thinking you didn't follow through with the SLAM.
Your done when
1 your water is crystal clear.
2 you have CC's of 0.5 or less
3 you can pass the OCLT.

 

[DivingIn]

I thought I did - I had the pool at 15-20 for 3 days, I did the OCLT with no drop in levels and no CC, and the water was (and is) crystal clear. I guess there is a possibility that the FC dropped to 12, which is the SLAM limit for a pool with a CYA of 30.

I'm thinking you didn't follow through with the SLAM.
Your done when
1 your water is crystal clear.
2 you have CC's of 0.5 or less
3 you can pass the OCLT.

 

[DivingIn]

Is it possible to re-introduce algae by means of the solar cover?

 

[Tom Tank]

I just went through the same thing with algae returning after a successful SLAM. After the algae returned, I SLAMMED again, but this time used Polyquat 60 after the FC levels went down. My pool has been clear even with heavy bather loads and FC creeping close to the minimum for my CYA level. I did do everything by the book - brushed twice a day, backwashed regularly, vacuumed, brushed behind lights and all around ladders etc... I guess the solar cover could re-introduce it, but I am a new pool owner and would leave that question to more of the experts on the forum.