idk what it is

So I am emptying my entire system after about 5 months running… and I find this in the sump it sat stagnant for about 20 hours give or take. It’s looking like a sheet of mucus or plastic but it’s in a shiny clear sheet… but it is in a few different places. I only had a poly(which gave me a run...

My angelfish (coral beauty) is laying in a hiding spot, still alive and on its side. What do I do to keep her alive, and get her back to health? What is this?

So im new to saltwater. Ive had planted tanks and even have a 45 gallon ciclid tank now. Just so recently decided to take the plunge into the ocean.. I have a 10 gallon nuvo compleatly basic setup. Still in the cycle phase only had the tank up for a week but when adding live rock i found a crab...