No. They lost a third of the FC from 15 to 10, so theoretically if they started at 6 it would drop to 4. Assuming the loss was only to the sun.I am concerned your FC on may 8 was 15 in morning and 10 at night, loss of 5 during day
if you are targeting fc 5 that would mean fc 5 in morning and fc 0 at night?
What times were you performing the OCLT? If algae is coming back that fast, you did not pass the OCLT.
Can you post some pics?
What is the pool surface? Concrete with plaster? Painted?
I suggest that you raise the SLAM shock level to 20. Remember to brush every nook and cranny. If you have light fixtures, you should check behind them for algae.
And, after this SLAM is completed, I suggest that you maintain FC between 4 and 6, and never below 4. How and when have you been adding bleach during maintenance? It is preferable to add FC in the evening after the sun is off the pool. That way, all chlorine goes to fight any organics and none is wasted by sunlight.
Keep posting and we'll figure this out.
Yes.Re algae possibly behind the pool light. Can I just unscrew the light fitting to have a look. Presumably I should cut all power to pool room.
I will try to take some tomorrow.Yes.
What about some pics?
Why did you stop the SLAM from 5/11 post #67? You note that you bring the FC back up to 5ppm. This is why you are not passing and breeding a BLOOM.
Your pics in post #74 look cloudy. It seems that you are seeing progress and letting it go thinking it's good enough. What have all of your OCLT results been? Are you meeting the 3 criteria of 1ppm FC loss, .5ppm or less CC and crystal clear water?
You are finished with the SLAM when....Will do for two more days.