Well. Nice tank!
And let's hope the Nem makes it! They can be glass babies sometimes, so keep fighting for it, don't worry too much.
Okay, let's see if we can get obvious things out of the way.
You know already that the bleached nem will not get energy from light right now? If you see the bleached Nem pull completely in during the day time, it would be good to place something over it to dim the light for a few days and see if it comes out to "fish" for sun then. Do you already know about feeding schedule for bleached nems? And is your water generally something you got a check on, so we can assume you didn't overlook anything in water quality?
Okay, obvious things mentioned now, so we can go on to what I really wanted to say!
Nems kinda "sleep" at night and your Nem might just have forgotten to hang on.
Let me explain:
It have got no braincells, so it keeps all its memory of your tank inside it's fibers, as a physical imprint of how it was shaped yesterday instead.
It "felt" your tank on the first day, and pulls in its skirts according to what it "learned" about the light and flow conditions there.
So, the next day, what it then wants is to adjust its outer skirts with the pattern that it "memorised" yesterday...
(It has totally forgotten at this stage that it has been moved half way around the globe and now it is focused only on the direction of flow and light in your tank and how to place all of its tentacles optimally, in that light)
That makes it easy for the Nem to "forget" to actually grab on to stuff because it is literally focused on its skirts being perfectly shaped, and cares very little (in comparison), about its root or foot or what you call it. So it kinda forget that it is moving into a new place along the way and it lets go easier until the 2 - 3 days are over, where it essentially just want to place it's skirt out because otherwise everything is in disarray.
Nothing is more against the will of sea Anemones, than their skirts being out of order, apparently.
It's like a sun-fisherman.
It ain't got nothing to do but "put out" its net and "pull in" its net everyday, with the "memory" of where the skirt got Optimal amounts of sun yesterday.
So how it does it is like a machine, net out, net in, net out, net in, resulting in frustrated Anemone owners not getting their Nem to take a hold on anything and this makes the Nem give up by itself and die lying on its side in peoples' tanks.
I think you should just get your Nem physically trapped for some days and see if that is all it needs essentially. As long as it is still adjusting, I would say possible turn off one of your two powerheads, the one that cause most direct flow at its location and then try to physically trap it in the location you "wish" it to stay in.
Just move around anything in the display until you get it cornered and stuck and then move it back as you want it to be arranged after the Nem has had time (during it's sunfishing routines), to remember to attach it's foot more securely.
Good luck and enjoy your aquaria
