Ok, this is fine it will most likely move to a place where it is not on top of the palys. Also to clarify, If I had to guess it is moving to a place with better light and flow, your parameters shouldn’t be the problem.
Also, this species of nem prefers to attach to flatter surfaces. It might be in search of that.
I gotcha, well I appreciate you saving this tank, more importantly this nem, as if it is true about it being 20 years old, that’s a great feat and it would be terrible for it to be just thrown away.
Did your tank come with an RO/DI UNIT?
Do you have any pictures? Haha, sorry to ask that so much but a picture is worth 1000 words in the hobby. Hopefully I will be able to identify which carpet you have and if not I can tag someone that is better versed than I with that.
Also, moving forward when talking about nems, if the Nem is still attached to something whether it be a rock or the glass, I wouldn’t necessarily call it “detached” but rather “moving”. If a nem starts floating around the tank or is face down in the sand, then I would consider it detached which is almost always a bad thing. Moving just implies that it is in search of better conditions. And this is just to help avoid confusion.