My poor fish,,,, i need advice pls?

hi some of my fish are suffering from ick white spot, i have got treatment and have put it in the tank. i remover filter media as instructions said,an this kinda freaks me out like what about all my good bacteria, it sais to add another dose in 4 days , but didnt say to do a water change before or just add in another dose???? also 7 days are up i have to do a 30% water change so when i pit back in my media do i wash it in taken out tank water ,,, i am a relativley new takn owner bout 2 months all was great till i seen an infestation of ick, and iv put it down to last week when i bought 3 neon tetras i think they must have had it as they were the first to be showing distress,,, any advice guys is really appreciated as iv grown to love my fish ,, my tank is 200 litres an fish are balloon mollies , guppies, tetras, a rummy nose tetra, platys, neon tetra , sucking loach, pakistan loaches, and 1 gourami, thanx guys x x x x oh and i did a water change b4 i put treatment in an its been a few hours now an still a few fish are hovering at top of the tank not doin much,,,,, will they be ok do you think ??