Ich?

Hi. I have had a 10 gallon aquarium for about two months. I have an
external power filter, a bubble-wall, and a heater. My pH has remained
steady at ~7.6.

Over the lifetime of my aquarium I have had four fish; three have died
and the fourth has started exhibiting the same symptoms as the
previous fish. After about a week (today is exactly one week since I
got my most recent fish, a platy) the fish develop little white spots
on them; this fish has about six dots. I can also see A LOT of
floating white dots in the water.

I have read about Ich and assumed with the previous fish that that was
the cause. I raised the temperature of my water to 82-84 degrees and
used Ich Away. Still, the fish did not respond to the treatment and
died after a couple of days.

After the fish died, I drained the tank and let it sit dry for a week.
I boiled the gravel and set up the tank again. I let the aquarium run
without a fish for a week. I saw nothing in the water to suggest that
Ich was still present, so I introduced my current fish.

I have been testing the water nightly for ammonia and nitrites and I
have been doing a 30-40% water change every night to keep the ammonia
at safe levels. After a water change, I treat four gallons of water
and I let it sit for 24 hours in the same room as the aquarium so that
the temperatures will be close for the next night's change.

Last night, nitrites tested above zero for the first time and I first
noticed the white spots on fishy. Is this Ich or could it be something
else? I vowed to this fish on the way home that I would keep him
alive, so I want to do everything possible to keep that promise.
Should I raise the water temperature? Should I use Ich Away again? If
I add Ich Away I need to remove the medium from my filter, which I
assume hosts the bacteria I need in the tank. So removing the filter
seems like a bad idea.

Any suggestions are greatly appreciated!

Michael.