OT (somewhat) - Tank mirrors

Yes this is only related to a tangent subject, but it seems most things the
group in toto, is just short of the Encyclopedia Britannica's in overall
knowledge Originally started on this idea as a hospital or isolation
tank, but like ponding one thing grew to another and now we have a used 50
gallon tank Sorry I cant be more specific but it seems to have mirrors on
the inside of all four sides. If you look through parallel sides you can
see through as if there is nothing there. Look at a distance through
perpendicular sides and it appears to be a strong mirror on the far side ie
you look through one, the other is a mirror. If you get close and look
through perpendicular sides the 'occupants' seem reflected but objects at a
distance, (ecspecially when back lit) are quite visible, though 'filtered'.
Put your hand right behind the glass and it is barely discernable, if at
all. I was really bummed at first, because I thought this meant the fish
would be unable to interact with us, however now it is apparent they can see
us to some degree? Walk up and they will swim towards you. Put your finger
on the glass and they dont seem to see it.

Could someone give me a short remedial course in 2 way mirrors so we can
understand how well the fish are seeing us and under what circumstances?
No, I'm not willing to stick my head in the water to see for myself
Thanxx
Bill Brister