Wow, you've got a huge decision to make.
On the one hand, you have an outbreak of whitespot (ich), and need a medication to cure it.
On the other hand, you've got a huge nitrite problem - 1mg/l is INCREDIBLY toxic, you need to do huge water changes to keep that in check. But if you do those water changes, you will be diluting the whitespot treatment.
Effectively you have a choice of how you want your fish to suffer/die - not a pleasant choice to have.
Obviously, I've never been in that situation, so I can't give you advice from experience, but my instinct is to suggest that you do a 95% water change EVERY day, and dose the whitespot treatment every day, immediately after the water change, for 10 days.
I would also suggest that you turn the tank temperature up to 28degrees, and make sure that you have PLENTY of oxygenation in your tank. Turning up the temp will reduce the amount of dissolved oxygen in the water. Nitrite attaches itself to the fish's red blood cells, and stops them from carrying oxygen, so it effectively suffocates the fish. Many ich treatments also reduce the amount of oxygen in the water, although I don't know about your particular one. But potentially, you've got three different factors that are reducing the available oxygen to the fish, that's why you need to have as much aeration of the water as you can possibly get. Make sure the filter outlet is rippling the water as much as it can, and if it still isn't rippling much, get an bubble line in, which will make the surface ripple loads.
Don't stop using the treament as soon as the spots disappear, you need to keep treating, because there will still be parasites swimming around in the water.
Next, you need to read the green link in my signature area. If you have that much nitrite in a week-old tank, you are "fish-in cycling" and it looks like you don't know a huge amount about that. That link will tell you what you need to do to keep your fish as healthy as possible.
Good luck, keep posting your progress.
