Toad stool leather coral problems

[JacksonJigsaw]

Toad stool leather coral, 3 days
10,000k 18w nano cube lighting
nitrate 5
pH: 8ish
Temperature: 78
liquid test
mid tank
mild water flow
Explanation of problem: The first day i put the coral in it slimed and shed, no problem just stressed. now 2 days later it is starting to for small brown dots on it pretty quickly. there is also a smaller coral just a little farther down that is getting it to. is it algea? or slime? its only on half of it ( the side facing the power head)

 

[JacksonJigsaw]

 

[JacksonJigsaw]

UPDATE

the few brown spots over the course of four hours became a giat membrane of slime across the top. i lightly blew it off with a baster and the coral looks super healthy, no polyps yet tho!