White Spot Or Fin Rot

I've just got back from a weeks holiday and have discovered that one of my new tiger barbs has shredded fins - both his dorsal and his tail. I only have 6 tiger barbs in my 50L tank and they have been in it for 4 weeks now. before they were introduced i did a fishless cycle and waited until all readings were zero. My readings now are:
pH 8.0
Ammonia 0
Nitrite 0
Nitrate 5

The barbs are only about 1/2 inch long so are relatively young. They have also been flicking every now and then against the terracota pots i have in the tank, but this is strange as the water stats seem spot on to me. So although one of the barbs has shredded fins, it also looks like it may have white spot as i can see small white dots on the tail (where the shredded fins are) and a couple on the body. Is it possible he could have both diseases? Or could he be getting bullied by the other 5 barbs as he is the smallest and has since developed white spot? I have upped the tank temp to 28C and have dosed with methylene blue, as well as isolating the poorly barb in a bredding trap. Has anyone got any ideas?

I've tried getting a pic of the barb to show his fin damage - but as the water is now blue due to the meth blue, this is proving difficult. Here we go anyway.....
He is still eating but isnt looking any better. I would say he may even have some more white spots on him! Any ideas?

ok ... seeing as no-one else has replied, I'll give it a go. Although, I'm no expert so if someone else contradicts me listen to them! lol.

As far as i know white spot is often brought on by stress (eg: moving a fish from the lfs to your tank or a fish being bullied). So ... my logic would be to see if the other barbs have been nipping him at all. Tiger barbs do tend to be nippy fish and spend much of their time figuring out a pecking order between themselves so it could be that, as this barb is the smallest, he has been getting picked on a bit more than normal. That could explain the shredded fins (and i also think that nipped fins often go on to get fin rot) and the white spot could be the stress of it all.

Are the shredded fins red at all or blood streaked? if so its probably fin-rot.

I think that medicating with something that deals with fin rot and fungus is the best way to go.

And are the white spots raised or like cotton-wool. If so, it might be some sort of fungus and not white spot.