New Dwarf Gourami - Ich

I bought a new dwarf gourami last night and it has 4/5 white dots on its fins/body. Just checking its definitely ich before quarantining/treating. Also checking whether treatment I have is okay for corys.
 
Tank size - 70 litres
p/h, ammonia, ni, na - unknown as test kit run out. Tank has been cycled for over a year.
 
fish symptoms - got it last night, stayed in bottom hand corner, and has white dots on fins/body. This morning it is livelier and is exploring aquarium, but still has white dots.
 
Also I noticed a cory flashing, is this something to worry about.
 
water changes - usually at least 30 percent a week, 50 percent two days ago.
 
tank inhabitants - 5 cory trill, 4 neon tetras, 1 new dwarf gourami
 
recent additions - dwarf gourami and big java fern plant
 
Sorry pictures are so terrible, hopefully you can see the dots. Also included pic of treatment I have (contains formaldehyde and malachite green oxalate0. Has anybody used it and is it safe for corys?
 
Thanks
 
 
 
 

now I've seen a neon tetra flash! So I've just done a water change and tried to set up my quarantine tank, but it turns out the filter for the qt tank is making a really loud noise and I forgot that my other heater broke!
 
I suppose I sould just treat the whole tank?

I would treat the whole tank, yes. I would generally go for high heat + salt + lots of vacuuming before going to a medication but that is up to you.
Be sure to read the instructions carefully as some have different doses for fish like neon tetras, though I'm not sure why.
 
Hope they all get better soon

Most treatments have a warning on the back if they arent suitable for scaleless fish or inverts.
 
I wish you tons of luck, because my only time dealing with ich was horrible, though a lot of people seem to get it cleared up easily.