Anti Fungus And Finrot Interpet 8

I noticed that where some fins have been nipped on some of the fish they've developed 'white spot' fungal infection. I treated with Anti Fungus and Finrot Interpet 8 but I think need to do a water change as the ammonia is registering at 0-0.25 but interpet instruction leaflet has no instructions on what to do if you need to do a water change.

Can I get some advice please guys?

Thanks Colin, I'm on a rather steep learning curve atm, delighted to say the white spot has disappeared when I checked this morning.