Ill Guppy Tail Growth

A couple of weeks ago one of my male guppies died, his tail became clumped together and he was unable to swim properly. One of my other guppies has just started showing signs of this today, however his tail is not as clumped together as much as the other guppy. Is this an infection or fungus and can i treat it? I have a few other male guppies and don't want those to get this aswell! Thank you.

Is there any chance you could get a clearer pic?
It looks kinda like fin rot to me.

Is that any better? It seems like his tail is curling in on itself and going purple?

I'll stick with fin rot, but I might be wrong.
Here is a link:
http/www.aboutfishonline.com/articles/finrot.html

I can't quite tell in your picture.  If none of the fins is being eaten away/disappearing... and is more rolling and not unsticking... it looks like sticky fin to me (my betta gets this frequently when he rips his tail when the strands aren't able to be filled out during growth.  Sticky fin is a fungus problem.

If that is the case, a fungus and finrot medication treats it very well.