Mysterious fish ailment

[Jabfish]

Hello everyone I am experiencing a unknown illness in my planted tank I have attempted to research it on the internet but I can't find it the fish develop a white film almost like they are producing excess mucus and slowly dying- it originally only affected newly added specimens but some of my older established fish are showing symptoms and 7 have died old fish all new ones are dying I have pictures tell me if I need to get more

 

[Jabfish]

I don't know how to embed pictures so if someone could enlighten me