Questions - Need some input

So here is the problem im having, someone or something in my tank appears to be eating my Acans :/
About 3 months ago i lost a ~7head frag, I thought I was safe till 2 weeks ago when I noticed one of the heads on another frag slowly vanishing and tell tale signs on another.....help
in my tank that i know of i have...2purple firefish, a rainford goby, 1 big turbo, 1 emerald crab and lots of these pesky white star fish that like eating GSP...i think ( thats my next post)
below is ...

i need some advice, today as I was doing my water change I droped a piece of eggcrate that had a frag someone gave me right into the L T A.
I was not able to see where it went at first, then a few hours later I was able to see a section of white sticking out of the mouth.
what if any can i do

I have been looking pretty heavily at making my own lighting for a new 75 gallon tank I just got. I'm debating whether to make an LED fixture or use MH lamps. I am wondering what the light output need would be for a standard sized 75 gallon (I realize LED and MH are different so whichever you guys know more about, please fill me in!). I would like to ensure that I can care for SPS corals adequately (the tank is 21" deep). Also, I am planning on hanging them 6 - 8 inches above the tank if ...

Posted wrong picture, this is the right one's

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please tell me what this is , only come out at night did not put it in there

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