whats this ?

good evening to all my first post :Cheers:.
i have a 125 gl tank with a coral insert and plenty for now live rocks,i have 2 clowns a blue tang,dotty back,2 emerald crabs and 4 hermit crabs in there now for about a month,my tank is under 4 months old.i have 0 nittrite,0 nitrate,0 amonia,i`ve done my 20% wc last week,i use my ro/di 5 stage BRS to make the water.but i keep seeing this white stringy fuzzy looking slime on my coral insert only not on the live rocks or the sand bed just on the fake coral can anyone help i.d. this i`ve been looking everywhere for any info and have found nothing.i`ve tried to physically remove it but most of it just breaks apart and get blow around the tank. thanks in advance to everyone.

Looks kinda like vermetid snail slime. Not sure though. Is it possible the insert is leaching something to make algae or fungus grow?

Welcome to the forum...
I'm pretty new to salt water aquariums and I have some fake coral pieces in my tank, too. My tank has only been up a month and I haven't seen any of that yet. I do however see something similar in my freshwater tanks on the 'rubber' part of heaters and their cords. I don't know what it is and I just rub it off.

i will look into that, i plan to eventually replace the inserts with the real stuff, thank you for the help.

i was told at lfs that my problem could be my airfreshner that i have in the same room, so i moved it out.. and 2 days later the white stuff is gone but now i have what looks like lite brown dust on my sand in some of the tank?

sounds like diatoms, very normal in a new tank and should go away as long as you arent using tap water, or have a silicate based sand.