Chlorine level good, but still green

So, I get pool to shock ing level, clears up then maontain cl to above 3 but water still turns green within 3-4 days. This is even with out pool use ..temperature has been in upper 90 ' s to lower 100's. Pump running 12hrs a day and sand filter backwashed accordingly. Any ideas? Other than shocking, I maintain it to above 3 cl with tabs. The cya is between 40 and 45. No cc last time I checked. Pool is about 20k gallons but I round up to about 24k to be safe. Sand in filter is new. Dont brush as much as I should. But I thought the walls and floor would show that thier dirty, not the actual water. ThNks for any advice.

According to the best guess chart, 3 would be the bare minimum. You really should try to keep it closer to 5 or 6. That way you would have a bit of a buffer zone in case something tries to get started, as it seems to be trying to do. When you shock your pool, are you keeping it at shock level until you can go overnight without losing more than 1ppm? If not, then the algae tends to come right back, because you haven't killed all of it.

what charlie_R said!

also are you checking that CYA yourself? you mentioned that you are using "tabs" to chlorinate. do they include stabilizer? if so that CYA could be higher than you think. i would double check/test those CYA numbers just to be certian. i would also shock to make sure you are getting rid of all that algae that keeps coming back, like charlie_R mentioned with out losing more than 1PPM of FC overnight, then dose as needed based off your CYA numbers.

When you shock the pool to get rid of the algae, you have to keep it at shock level until ALL of the algae is dead, including what you can't see. If you don't, then it keeps coming back, as you've seen. Darkside and Charlie have brought up some good points--keeping the pool shocked until you're no longer losing chlorine at night is an important part of this process, but verifying that CYA level is probably a good idea.....

When you brought the chlorine up to "shocking level", what level did you bring it to, and how did you measure it?

Sorry guys, been out for a while..makes sense..when I shock I bring it to 15ppm or more..the other day went up to 30. I use the taylor k 2006 and test my own cya of course. I use tabs and rea alize cya can go up but keep my eye on it's

When I shock it I do it att night. I then run the filter 24/7 until water clears up. Usua lly over night already see a big dif
differemce. but; I dont bother to check the chlorine afterwards, that is once I shock im pretty sure it will clear, but then greenish again within days. Never slimy and sticky walls or floor though. Th ere seems to be loose orange ish dust cludy deposits on floor but never slimy..thanks so much

You're just not holding it at shock level long enough....you need to keep it there until you're not losing any chlorine overnight, then you can let it drift back down.

Ok, been kee ping shock level up since tuesday. Shocking att night , checking cl, then checkimg cl in the morning. First couple days it was losing about 7 to 8 then last c ouple days days about 4 to 5. last night raised to 18 and this ,m orning , att 10am with sun already out (previosly was checkimg @ 6:30 am) cl was att 16 ..my question now is if I been using liquid cl would I anticipate for cl to be lost att a higher rate than powder cl? The pool water is crytal clear right now and cl loss from last night was 2. The previois night was about same loss also. maybe im done? Thanks

Liquid or powder chlorine makes no difference. It's just chlorine when in the water. Sounds like you are pretty well there with the chlorine level holding.