Sounds to me like your fish has fin rot and should be removed from the community tank to a hospital tank.
Add salt 1 tBS per 5 gallons of water.  Your fish may also have to be treated for a bacterial infection.  I would use melafix according to bottle directions.  If after 3 days you see no improvement then your fish will have be treated also with an antibiotic such as tetracycline.  Your aquatic store will have this on hand.
Good Luck! 

Hmm.....the test I used was "Quick Dip" by Jungle, I don't know how accurate it is, but just re-tested, (it tests for nitrate, nitrite, hardness, chlorine, alkalinity and pH) but it's not those little bottles, so I don't know if it's any less accurate, but the nitrite reading is apparantly off the charts.....    Nitrates @ 20, Nitrites over 10.0 if I'm reading it correctly, the square is pinker than any of the options on the chart, the pinkest of which is 10.0..... the water hardness is 150, chlorine is 0, total alkalinity somewhere between 80 and 120, and pH @ 7.8.......it's a 60 gallon tank, with a 70 gallon rated air pump which I have delivering air to 3 different areas, and the filter is rated up to 100 gallons, so I should be ok there I think.  There are a lot of live plants in there which I thought should be healthy, but is it possible to over plant? I also have added 8 Japanese Trapdoor snails about 2 weeks ago....but just talking to my wife and she confirms I'd been commenting about Coco's strange behavior since before the snails......a medi-tank sounds like a good way to go but is not really an option right now, unless I use a 5 gallon plastic bucket (?)

I don't think it is possible to over plant an aquarium... so no need to worry! Still, your water values sound a little bit scary. How long has this tank been up and running? It might not be completely cycled yet. So it might be good to get some biological filter booster! You need to bring these nitrite and nitrate levels down! It might be that you added too many fish too fast, and that their waste is overpowering the beneficial bacteria in your filter.

First things first, repair your water parameters! Doesn't it say on the test what you should do if they're too high/low?

Hm... so, to reduce the ammonia levels, you need to change about 70% of the water at a time, reduce the feeding, and possibly the amount of fish until the levels decrease. But since you have no test for this, you don't know if it's necessary... still change 50% before proceeding with the salt bath to keep the strength of the solution constant.
To help your fish survive a nitrite rise (which you have) add aquarium salt to a 0.3% solution, meaning one tablespoon per gallon, split up in three doses added every 12 hours. (Any live plants should be removed before treating with salt.)
Since your nitrates are at 20, you don't have to worry about this much for now, it's usually harmful when it's above 40 or 50 ppm, as it makes the fish more prone to disease and infections. Levels over 200 ppm are toxic to fish, and may kill them.
 
Getting a quarantine tank would be very helpful for treating fish in the future, and since you might need to have less fish in the current tank until it's cycled, it might be beneficial for you to get one... to speed up the cycling process, you should keep the water around 80 degrees Fahrenheit, and "feed" the tank with no fish in it. This will encourage the presence of beneficial bacteria. Of course, test ammonia, nitrite and nitrate levels of the new tank, and see to it that the ammonia is down at a definite 0 before moving any fish over there!

But, do try to repair the water levels first, I think it might be a bit much for you to get a second tank up and running just because of some water quality problems (:

The 70% change was for excess ammonia, which is most likely not present since the nitrate levels are so high. Don't worry C:

   no, I meant the filter is rated for a 100 gallon tank. But I was mistaken, it's actually rated for a 70 gallon. I don't know the GPH specifically, but images speak louder than words so here is a video of my tank.

(Link is not visible to guests. Please register to view.)	(Link is not visible to guests. Please register to view.) | (Link is not visible to guests. Please register to view.)

 I add the beneficial bacteria juice, and did another 10 gallon water change since last post.....I put Coco in a medicine "tank" bucket

(Link is not visible to guests. Please register to view.)	(Link is not visible to guests. Please register to view.) | (Link is not visible to guests. Please register to view.)

I am treating it with Maracyn. He/She (how do you tell?) seems more active now too, so hopefully it's working.
You can see the tail damage more clearly in the bucket film, and how it uses only the one side fin...

Absolutely gorgeous aquarium.
I think it may just need to finish cycling and Coco might have been weakened or stressed and the ammonia/nitrite spikes didn't help so he got a bacterial infection.  When fish are stessed they are more suseptable to viruses, bacteria and other parasites.  Looks like he is on his way to getting well.
I also see you have really good aeration going too. 

Lovely tank you have! I like how you can see the tube for your bubbler.. I have no idea how to hide that st*pid thing. ^^ Hope all goes well for your fishy