Nipping Tiger Barbs

I seem to be having a spate of non-emergengy issues with my fish at the moment, so I'm asking for advice again.

After upgrading the dwarf puffers I used the spare 125L tank for the tiger barbs. Initially they seemed very happy with it, and the extra fish. I currently have 19 tiger barbs (one passed shortly after purchase/addition), a mix of standard and green, in a planted species only tank. It has quite a strong flow at the surface and the majority of them shoal together swimming against the flow.
Today I have noticed that 2 of the standard tiger barbs have nipped tails.
I understand the heirarchy situation, but during research thought that the 125L/80cm tank would give them plenty of room, and that a large number of them (but only 71% stocked) would dissipate any agression.
Should I remove the 2 with nipped tails to give them time to recover?
If so, should I put them in seperate tanks to avoid them nipping each other, or can they go into the same hospital tank (70L, 60cm)?
What should I do with the main tank to avoid this problem again? Should I include more plants, or have more open swimming space? Should I put more decor in the tank to entertain them, like with the puffers?
Water parameters as tested on Saturday (pre-water change) are 0, 0, 40, as usual.
A few weeks ago I was telling one of the guys at the LFS that 2 standard barbs were nose to nose, sort of slowly spinning around, and I didn't know if they were fighting, then they moved side by side (nose to tail) and continued to spin. He said they weren't fighting and were actually pairing up. Could this have caused the extra agression/nipping?
Sorry to have to keep asking for help, but any advice is appreciated, as always.
 

Slightly more urgent issue.
I was watching the tank and noticed that one of the nipped ones was swimming strangely, and when it came closer to the front of the tank I noticed some fungus on the nipped tail. I've put him in the hospital tank and given the first dose of esha2000. Not holding out much hope as it seems quite wobbly/weak.
I'll do a water change on the main tank, and then perhaps 15-20% every other day, if that is going to help.
I'll try to get a closer look at the other nipped one to try to work out the sex.

I think that course of action to isolate and dose with the eSHa 2000 sounds sensible, in light of the fungus as well. Scrupulous water quality is important in such circumstances, so a small water change every other day as Sue/you suggest does sound sensible.

[I have Melafix as well - although it's only like a disinfectant, I found it useful as a "halfway house" when undecided whether to isolate and treat my pygmy cories with eSHa 2000 or whether not to treat ie I just put a small dose of it in the main tank as it's very mild and so wouldn't have adversely affected the healthy fish.]

Aw- really very sorry to read of this. 

Whatever is going on, it seems that there's nothing more you could have done ie you tried treating one, but the outcome was the same for both the treated and untreated ones. Hmmm... not sure what to suggest here...

I started with 10 green tiger barbs in a 120 litre tank with other fish. I now only have four left, the others having been subject to the same thing, i.e. incessant tail nipping which only started when the fish matured.. I began by moving the badly affected ones, as I noticed them, into other tanks, but in spite of this and treatment they all died. I think it's the combination of the nipping, with possible infection, and stress that kills them. There is only one male left, he now has the three females to himself and is extremely large and brightly coloured, definitely the alpha male.
My Black Ruby barbs have a similar problem but seem tougher, I still have three males and five females of the ten young fish I started with. Two of the males have bitten tails but they still seem otherwise healthy and have been like this for two years now, they seem to be much more resilient than the tigers.
I won't be getting any more of these barbs in any future stocking,  prefer the more peaceful types. In spite of strong inter-male rivalry among my Emperor tetras, they all still have their beautiful tails intact!