Good catch.

The answer is simple: Intex is wrong. Intex is basing its recommendation on old government warnings which were nothing more than a bad guess on the Fed's part.

At the same time they were saying you shouldn't swim in water that was higher than 3ppm (of chlorine), they were saying you shouldn't DRINK water higher than 4ppm. See what I mean?

You have a serious algae bloom and you need to kill the algae. Getting your chlorine level to 15ppm and keeping it there is the only thing that will kill it.

You do NOT want to swim in an algae-laden pool. Seriously. If there's algae, all the chlorine is being consumed fighting it. That means there's none left to fight bacteria, viruses, or the traces of fecal matter than EVERY person leaves in the pool. (I know this sounds gross and disgusting, but it's true--chlorine neutralizes that stuff and makes is safe and clean).

Algae itself is not dangerous to you (to the best of my knowledge) but if it's growing, ALL your chlorine is spent on it and the water is now ripe for contamination.

Once the algae is dead, the chlorine will sanitize everything else.