my first acro

With mine, the RTN made the tissue just slough off in pieces. I could see bits of the tissue barely hanging on to the bone and moving in the current.

If it is RTN, you should frag the acro right away and try to save the healthy parts. RTN is contagious, so it's best to deal with it right away.

 

is it contagious to montis?

 

no its not contagious between different genus

but this is how acros act when first introduced into a tank.
first acro added: doesnt do too well, usually looses all or most tissue
second acro added: may have a little rtn at first, may be lost completely
third acro: maybe a little rtn, if any
fourth and subsequent acros: not much rtn unless they are just really finicky

this is not true in all cases, but with all the tanks i have seen set up, this is how it has happened. With the experience gained from taking care of corals for long periods of time, you can reduce the occurrence of rtn/bleaching down to none at all if your good

also, in the first post you stated that you had a powerhead aimed at it... maybe try backing it off a little. acros flow should be dynamic (circular) as compared to linear (straight line) and come at it from random directions at different times. try bouncing the flow off rocks and glass before it gets to the acro