diseased fish in a clean tank.

Some of you regulars might remember this thread from a few months back. I
had a nice clean tank that a diseased fish that I did pre-quarantine
infected, and all the fish died quite rapidly . I got some invaluable
advice and warnings from several people here regarding Potassium
Permanganate, but the fish had all died before I got the Permanganate in
hand.

Here is an update:
After about 7-8 weeks empty except for the crabs, snails and starfish, I
started restocking the tank. All well and good, all fish are happy, blah,
blah. This was some time ago. Well, today I notice that the Fridmani has
signs of fin rot, and a couple of very slightly "mildewy" looking spots on
his side. Just like the last time. And the Scissortail goby had it as well.
So, knowing full well the risk I was taking, I decided to blast with
Potassium Permanganate instead of dissassemble, catch fish, and reassemble.
For 80 gallons, at a dose of 2mg/L, the math said use .6 grams.

"Grams of Chemical = Gallons Treated × 0.0038 × 2 (mg/L)Therefore, to
treat a 250-gallon vat, the grams of potassium permanganate needed are
as depicted below:

Grams needed = (250 gal) × (0.0038) × (2 mg/L) = 1.9 gramsAn
inexpensive gram scale can be obtained by purchasing a dietary scale
at your local grocery store or pharmacy. One level teaspoon of
potassium permanganate weighs about 7.0 grams."

I did the math twice (80x0.0038x2=6.04), and calibrated the scale. Measured,
mixed with R/O water and dumped it in. The fish and snails were unaffected,
except the lawnmower blenny and the flame angel did that "scrape the head on
something" maneuver a few to several times each, which was not surprising.
They have not repeated the behavior. All other fish acted unnaffected, but
the goby went to sleep since it was dark purple in the tank. The inverts DID
NOT like it at all. All the hermits drew as far back in their shells as they
could. The Green brittle star completely dissappeared. I've never seen him
hide that well before. The purple lobster came out and waved his arms around
like he was cussing me out, and withdrew in to the rocks. He repeated this
two more times, then went and hid.

4 hours later, I add activated carbon and when the water got clearer, looked
for unusual things. I have killed my purple lobster, poor thing. The hermits
seem to be OK but a little sluggish. There were the very tips of the
starfish "arms" poking out of the rocks, so I laid my finger on one. Very
little reaction, which is bad. Nornally Ringo whips his arm around my finger
and tries to pull himself toward me. So, I brought out a bit of scallop, and
laid it on the arm, no reaction. This is really bad. So I push the scallop
into the bottom of his arm and he slowly wrapped around it and pulled it in
for consumption. I tried to feed him again, but he is having trouble. If he
were a human, it would be like someone who had drunk a fifth of whiskey and
was trying to pick up a paper clip. He tries, but seems really
uncoordinated. But he seems a bit livelier than before, so I'll keep
offering him scallops. The hermits and emerald Mithrax crabs are grooving on
what he drops anyway.

So, for my tank and Potassium Permanganate compatibility: Fish - Yes, no
problem. Snails - Yes, no problem. Hermits seem to tough it out and recover
quickly. Purple lobster - most definitely not compatible at all (maybe a
lower dose, but I'm not going to do it again with a lobster or starfish in
the tank). Starfish - No. Although he seems to be on the road to recovery.
We'll see.

No anemones or corals yet, the halide light fixture arrives tomorrow. Those
things ain't cheap.