mustard algae, pollen, or ecoklean

I am trying to figure out what keeps forming in the bottom of my pool. I was first told it was mustard algae. So we shocked the pool, waited 1 hr, poured in a bottle of banish, waited 24 hrs, backwashed to waste, took apart the EC75 DE filter, cleaned the fingerlings with kleen it, put it back together, added ecoklean. THe next day, the sand-looking stuff was back.

Another pool store told me to bring in my fingerlings, that ecoklean is getting into the pool.

Another store told me it is pollen.

How do I figure this out?

Thanks.

#1, stop listening to the pool stores! :)

If you will measure your chlorine level at night after the sun is off the pool, and then measure it again the next morning before the sun is on the pool and compare the two, it will answer that question for you. If you've lost no chlorine overnight, then you don't have mustard algae, or anything else the chlorine needs to clean. If you've lost more than 1 ppm of chlorine overnight, then you probably have algae and need to shock the pool. But to kill mustard algae, shocking isn't going to be a one-time thing--it's going to take shocking to the right level and maintaining that level until it's dead. Take a look at the best guess chlorine chart linked in my sig for more info....

When you shocked the pool, how high did you take your chlorine level, and what is your CYA?

Mustard algae can
+ looks like greenish or yellow powder on the surface
+ will brush away freely
+ returns within 24 hours, unless the chlorine is very high
+ tends to appear in shaded areas of the pool.
+ will never be on the floor of the pool where people step.

I have no idea what ecoklean is; pollen will be in piles or ripples, not an even film of powder.