I don't know how many others have had/are having persistent algae problems. But for what it's worth, here's what I think is happening in my case.

Where have your hoses been? What have they been used for, prior to filling/adding water to your pool?

In my case, these hoses that we've been adding water to our pool with have been used for draining flooded basements.

Here's what's happening:

I get the algae killed, as in no overnight drop in FC, no CC. Then I add water to the pool. Next day, the algae is back with a vengeance.

If this sounds familiar, may I suggest a 50% mix of chlorine & water, poured into your hoses and left sit for a day with this in them. I'm thinking that the extreme amount of bleach in the hose would give extra killing power, without depleting to the point of "almost enough" to do the job.

Several times throughout the day, circulate the water in the hoses by simply lifting the hose and running the loop all the way around back to the coupling. If you left any air in the hose (hard not to!), the bubble will move the water around.