Ok here is what I was looking for:
So Nems can bleach for two reasons:
1. Too much light too fast, zoos go crazy and they end up spitting them all out.
2. Not enough light and they spit out most all of their zoos because they can't maintain them.
I see in your second to last picture, once upon a time he was green and close to the bottom of the tank. I can't tell exactly where he is now, but I think still somewhere similar?
In my opinion he needs two things, stable living conditions, which you're finally giving him and better light. Now luckily your light can barely get there, but you're going to need to have him towards the very top of the tank. I generally try to shoot for around 200ish par at minimum for BTAs.
BUT WAIT
your nem is bleached, this adds a very important variable. You're going to have to adjust him into the light slowly. If it was me I would pick a spot somewhere around what should be the 100-125 PAR range so say like 12 inches below the light, but somewhere that gives him the option of moving closer or further away.
BUT WAIT AGAIN
He's just now coming out for one of the first times and opening nicely. Which is not a bad thing. The first pictures show a perfectly happy Nem that just happens to be bleached. If you measure how far from the light he is you can estimate about how much PAR he is getting. Typically when Nems are unhappy they will move around constantly.
So here's what I would recommend:
1. Measure and see what PAR he's getting. That will help us a lot.
2. I would monitor him for the next 72 hours to see if he moves again, or possibly you can tell us how long he has been in his current location? If it's been over a week then we may consider moving him, if it's only been a day or two, it might be best to leave him where he is for the time being.
Ideally the end goal here is you're going to need to get him higher in the tank into more lighting to get him to color back up. The tricky part comes in whether you have to physically move him or he will move himself.
If you end up having to move him I would probably try here first:
That should put him close to the PAR range we're looking for, give him a place to stick his foot under and attach in that little recess and hopefully extend out beyond that rock. Ideally he'll regulate his light by himself and retract under that ledge when he's had too much light and stick out when he wants more.