my chlorine is good but water is green

Can anyone help me understand where things went wrong for me? :(

I've been maintaining the chlorine at about 3ppm with my SWG and things were going great. I had the solar cover on the pool the last three weeks and maybe didn't brush the sides as well as I should. Took the cover off last weekend and found the water is a bluish-green, so it isn't too bad YET. I added 3 gallons of bleach and brushed it well today. Lots of green came off.

Here are my latest results:
FC 7, CC 0, TC 7
pH 7.5
Alk 90
Cal 190
Cya 40
Temp 80 F
Salt 3000 ppm per Autopilot recs

I could be wrong, but I was told that keeping your cover on for any extended period can let the algae start a bloomin.

Help? Anyone?

One thing I didn't mention, if it matters. I added the chlorine at about 10:30 AM but didn't do the water testing until about 6 PM.

river-wear: Having just done battle with algae myself, I feel I can pass along a few thoughts.

With FC of 3 and CYA of 40, your shock level is 15. Using the Bleach Calculator for your size pool of 27,000, it calculates that you would have needed 5.4 gallons of bleach to raise your FC 12 ppm (from 3 to 15).

Shock your pool, continue to brush, run the filter 24/7. Test as often as you can, 2 or even 3 times a day if you can manage it and bring that FC level back up to shock each time. It'll clear.:)

As to why it happened when your #s look good...maybe CanuckPool is right. Otherwise, algae spores are everywhere, even in "perfect" pools. Algae happens :D.

Thank you both for the help. I battled algae earlier in the summer, and you're right about needing more chlorine. I need to pick up some more at the store. Has anyone noticed that the "gallon" size bottles actually only have 3 quarts in them?

Mostly I was wondering about why the algae grew with 3ppm Cl. Canuckpool must be right about leaving the cover on too long. I didn't realize it would be a problem because last year the cover was on 6.5 days out of 7 - the pool guy (which I don't need anymore thanks to this forum) - would leave it off whenever he came.

We left ours on at the end of the summer for about 4 days in a row, no one was swimming and the weather was overcast. Didnt get any blooms but noticed that my Chlorine level kept going up and up (SWG set at 40%). The Pool store said I should keep the cover off during the day to prevent this especially if no one is swimming, they also mentioned something about having the cover on could cause algae to start. I suspect I didnt get any blooms due to a south facing pool and my pump was running 24/7 at the time. I guess even water needs to breathe.

river-wear-

You stated that you are not sure why the algae started in the first place. Could it be that the FC reading is the "highest" it is during the day?

I have my pump/SWCG run for 2 hours in the wee morning hours (this is when I add chemicals), and then run an additional 4 hours in mid-late afternoon. Before the pump kicks on in the morning my FC=3-3.5 and after the pump runs for about an hour or so FC raises up to 5ppm.

Could it be that your FC dropped down to ~1-2ppm? If so - that could have been enough to start the algae?

Simmons99, I'd say anything is possible. I usually run the filter 10am-4pm (10-6pm when it's hotter) and check the chlorine level at random times - but always after the filter has started.

Once I clear up my bloom, I'll experiment with this and see how much variation I get. My SWG has been running at 36% so I didn't expect large swings.

I've also been meaning to change the timer settings so the filter would run in two time blocks, which would also keep the Cl level more steady. Guess I'll get "around to it" very soon, especially with cooler weather and shorter filtering time on its way.