New tank clown fish problem

What i meant was to take a different approach and reconsider every decision that was previously made in setting up the tank.

 

I'd agree I have a tank that on reflection is too small to properly set up a marine environment but I got to where I am by buying the marine conversion pack for the 60L biorb and following the instructions to the best of my aility.
I'm trying to avoid getting rid of the fish as I don't know anyone with a marine tank and I don't think the shop is going to accept them back.
Which means a bad end.
The tank salinity is fine, temp is fine according to the info I have- the water does come from a tap and tap safed before adding salt and getting to right temp before adding.
I don't have the option of a bigger tank at the moment.
Wouldn't mind knowing what the clown fish is suffering from..

 

I now feel totally out of my depth!!

 

Added info

 

Perfect. Well, I searched a few sites and couldn't find any info on any disease in particular, but to me it looks like a good old fashioned infection. With an infection it probably won't heal up until your ammonia and nitrite levels come back down. The reason for the spike IMO is the tang - They produce a large bioload and it will take some time for you bacteria to catch up. Seeing as how you've pretty much limited your options as to what you can do with these fish, try putting your tang up on a website like kijiji or craig's list. I'm sure there are some marine aquarium keepers in the neighbourhood or their wouldn't be a LFS selling the fish.