How to restart (after a huge disaster)

Hi,
I was given a couple of goldfish (a bubble eye and another one
which was orange and white) by my officemate about five months ago
together with a 10 gallon tank and some very basic starter equipment. I
didn't know anything much about goldfish at all and made some huge
mistakes in the beginning. This included changing 100% of the water once
a month, not changing the water once for seven weeks etc. Amazingly,
they survived through all this though both usually used to sit at the
bottom and mostly swim only when they were fed. Otherwise, they seemed
ok (except that the bubble eye's bubbles became unbalanced - bad but
nothing to compare what was to follow). This was until about three weeks
ago. About a month ago, my roommate gave me a small pleco to add to the
tank. The pleco seemed to like its new home (there was a -lot- of brown
algae on the surfaces of the tank) after some initial stress.
About two weeks after this, the bubble started to eat much less.
I read up a bit on rearing goldfish on the web and started using a
gravel vacuum to make partial changes and over the next few days, added
a bubble curtain and started using "Start Right" with the water changes.
I noticed some white "grains of salt" on the bubble-eye and applied some
"Quick Cure" from the pet shop as well as 2tbsp of salt. The next day, I
noticed that the bubble eye also had a huge red patch between the
bubbles and small red patches were just beginning to appear on both the
other goldfish (now very inactive) and pleco (still fairly active). At
that time (about 5 days ago), I got Maracyn-2 and started the fish on
that and added another tbsp of aquarium salt to the tank. I only had an
ammonia test kit (no nitrite) and regular tests since then showed zero
ammonia until today. Soon after, the pleco's red patch seemed to
disapper (within a few hours) but it died very soon after I changed the
water the next day (I was doing 30% water changes every other day after
starting the Maracyn-2 since I got rid of the activated carbon) - it was
floating on top dead. Yesterday night, the bubble-eye died (did a water
change yesterday). Since the Maracyn-2 was not working and it was
getting to the end of the 5 day course, I thought of making a last-ditch
attempt to save the other goldfish with some Maracyn today. I did an
ammonia test and for the first time it was positive (0.5 -1) so I
immediately did a 50% water change and put in the last dose of Maracyn-2
and the first dose of Maracyn. This last goldfish was until 2 days ago
eating small amounts of tubifex worms out of my hand (it would not eat
if the food was not directly in front of it) so I still had a bit of
hope left. However, immediately after the water change, it swam
(struggling) to the bubble curtain and stayed there. It generally seemed
out of air and died a couple of hours later. While clearly sick, it
didn't look like it was on the verge of death before the water change.
This brings out a big question. The "Start Right" that I bought
was purple in colour and my big doubt was that it had a bit of potassium
permanganate (only purple chemical I know). I was adding about 2/3 tsp
of "Start Right" to the water before adding it to the aquarium. Now, I
know potassium permanganate will reduce the available oxygen to he fish.
So now, I am wondering if the "Start Right" contributed to the death of
the fish since they seemed to die quite soon after the water changes
(atleast the pleco was probably asphyxiated and as I sadly watched the
last goldfish die today - it was clearly asphyxiated).

I am still thinking of getting some new goldfish (yes, I seem to
be a goldfish killer but I think I have learnt quite a bit over the last
few days and will be more careful now) and don't want to repeat these
mistakes so I am going to read the FAQ and would appreciate any advice
and really want to know if "Start Right" contains potassium permanganate
(they should have a warning about this - there are no ingredients listed
on it). Thanks in advance for any comments.

Srikant