Yes, if you want to try something, add another dose of bleach and then turn your filter off. I want to leave it off for 2 full days.

Here's what I think may be happening. The Tagelus 50 is a shallow bed 21" sand filter. It's rated at 50gpm, but in reality, should never exceed 35 GPM. I'm not sure what 3/4HP pump you have, but if it's something like a Pentair Challenger 3/4HP . . . you're probably running around 60 GPM, or nearly double the never-exceed rate.

There's a LOT of back-story on this that I can't go into right now. But what I'm beginning to suspect is that blowing dead algae THROUGH a sand filter actually breaks the algae particles into even finer particles . . . and that after they've been broken, they not only cannot be filtered with sand filters, they are difficult to filter even with cartridge or DE filters.

There are two sorts of solutions here: preventative and curative.

+ To prevent this problem in the future, we need to make sure flow through your system NEVER exceeds 35 GPM, except when you are backwashing, and that it never exceeds 45 GPM even then.

+ But, to cure the problem, we've got to find a way to get the algae out BESIDES filtering . . . because if I'm right about all this . . . you can't filter it, now that the high rate flow through the sand has shattered the algae particles.

So, I want to try this
1. Make sure your chlorine is 20 or more this evening, and that there is NO live algae left.
2. If so, turn your pump OFF, and leave it off.
3. Check chlorine levels tomorrow PM, and make sure they are 10+ . If not, add a gallon of plain 6% household bleach.
4. Check Monday am, and see if there has been any change. Let me know what you see.