Fish Keeper begineer

Hello,

I've recently bought myself 4 goldfish. I bought the tank, waited a
week, bought two fish, waited a week, and bought two more. I noticed
the smallest of the four, bought in the second batch was very shy and
only came out to eat, then it died, three days after purchase. I've now
noticed the other fish I bought in the secnd batch becoming very shy.
the first two fish do tend to bully him a bit. I was watching the
yesterday and noticed white spots. I've googled and discovered all
about ich.

I went straight to the shop and bought some Interpet 6 anti white spot
plus treatent, but the leaflet that should be inside is missing! I'm
going to back to the pet shop tomorow, but in the mean time can any one
help with dose and advice for this product? I have a 21L tank with a
stingray filter.

Hopeing you can help me and little shamu the fish.

Katie