For the last week I've noticed when I brush the pool there is a greenish cloud that swirls up around the broom. I've never let my FC drop and even in the hottest summer months, when I'd suspect algae would be a bigger problem, never had this occur. The pool water has cooled considerably to mid-70s and I started noticing this. I wouldn't even know it's there except for when I sweep. The pool water is crystal clear.
I tested tonight and have no CC, FC levels were around 5. (2-6 is my ideal level according to PC). I'm stumped as to why this is a problem all of a sudden.
Anyway, I brushed the whole pool, brought it up to shock level (actually overshot it by quite a bit), and will test again in the morning to see where I'm at. My ideal shock level is 13. I added what PC estimated but ended up at 18 ppm FC. Since I've got plenty of wiggle room, I figured I'm probably ok not testing again tonight and will see how much FC I lose overnight.

I just find it odd seeing as it has been "cold" here in Central Fla. and I managed to survive the hot summer without a bit of algae. Just frustrating.

Posting a complete set of water test results would be very helpful.

Fc- 18 (now) was around 3 this morning before I decided to bring it up to shock.
CC - 0
pH 7.5
TA - 75
CYA - 30 (checked last 2 weeks ago but am not using Trichlor any longer, just bleach)
CH - 310

The TA was around 110 a few weeks ago and I brought it down because I was having a problem with pH rising so quickly and had read here that some people were more stable at lower TA levels so i thought I'd try. I do have a lot of aeration with a waterfall so the pH climbs very quickly. I add acid every 3 days or so.

Chlorine loss overnight was 5 ppm So, something organic is eating it up. I'll keep it up at shock level for now and keep going. I just brushed the pool again and again another green dust lifted off the bottom.

Hi, Cara,

I understand your frustration. You have a good grasp of the chemistry and certainly looks like you have kept your FC up where it must be so your resultant algae doesn't make much sense.

There are s-o-o-o many variables in pool water management that sometimes you just have to shrug your shoulders and say, "Oh, well!"

I'm sure you will get the algae killed quickly and get your pool all cleaned up but I wish I could shed some light on how it happened in the first place.

Thanks. I'm just going to keep chugging along.

Question, though: Right now I have my solar system shut down because we aren't using the pool that much. Should I open the lines and let the shock water flow through in case there is algae spores in those lines?

I wonder if there is some place that doesn't get much flow. Creating a pocket where the Cl gets used up faster then it replenishes. Do you have a main drain? How do you aim your jets? What is your pumps run time?

I would. And any toys or tools (skimmer, leaf rake, etc) that get used in the pool should also go in for a soak while it's at shock level. Run everything. I have a booster pump on my spa that I never use, but I run it from time to time just to keep the water circulating everywhere.

We do have a main drain. I have the suction set halfway between main drain and skimmer just because that's the level where the vacuum works best. I'm going to shut everything down and drop the vacuum in.
I haven't touched the jets since we moved in and it doesn't appear they are easily adjusted. I have to figure that out. once I see how they are aimed and look for possible dead zones.
I have a feeling this was never a problem for the previous owner because he used tabs with algaecide in them and shocked every 2 weeks like the pool store recommended.
We're having a SWG and new Intellitouch system installed in a few weeks. I did find a pool guy in my area who is not delusional like others I've spoken to so I'm going to ask for his help, too, if I can't figure this out myself.
The pump (an Intelliflo VS) runs 8 hours a day on speed 3. Again, I haven't messed with pump settings since we moved in because previous owner had it set up and it appeared to be running without problems.
Now that this problem has popped up, though, I have to start troubleshooting this system and looking for possible problem areas. Thanks.

Will do. We have a booster pump as well for activating waterfall to pool when in spa mode. Time to turn everything on! Thanks.

I went out and adjusted all the returns to get a little more surface agitation and direct the water out of possible dead zones. I know where the floating thermometer tends to "hang" so that corner might be a possible problem. I also noticed the return under our waterfall had some algae on the underside of it. I turned it and tried to direct water out of that corner.
We'll just keep testing and wait and see.