Weird algae?

[Ebenm]

So a buddy of mine started a reef tank with fish after seeing mine for a while. They made a mistake and somehow something toxic got into the water. He gave me the dying stuff to see if I could save it. Most of the stuff was too far gone and everything died. I kept the corals incase they may be alive in a bucket. I put them there just over night with heater. I woke up in morning and there is these weird roots at the top of water. Maybe strings would be better description? I’m just curious what they are and I’m assuming my corals are now dead? Let me know what y’all think. Not sure how well the image will come out, first time doing this lmk

 

[Big G]

Sorry can't see much on this end. Might be filamentous algae.

 

[Ebenm]

I wish I knew how to get a better picture on here. It doesn’t let me attach images

 

[Big G]

You can test to see if it's an algae by applying a bit of 3% hydrogen peroxide (this is the normal % found in stores). If the fibers dissolve, they are algae.