Discoloured Molly

[Gemmzy]

We added a white balloon molly to our 25 L tank about a week ago and in the past few days she's been turning a greeny-yellow colour around the head and back, like there's algae growing on her or something 0.o (see picture). She also has a few tiny black dots on her body, you can't see them in the photo but they look a bit like ich but black. Could they be black spot disease? Because from what I've read it more commonly occurs in saltwater fish...? Anyway all water properties are on track except PH is a bit low. I'm thinking the water may just need changing as it hasn't been for a while but any advice would be much appreciated as I'm quite new to this

 

[HUKIT]

I don't see anything concerning from the pictures, of the fish is eating and behaving normally I wouldn't worry.