Fin Rotted Guppy?

[fionah]

Please let me know if this looks like fin rot, and if so should it be treated with Melafix?

I have had my tank running for several months and have the water tested regularly (all zero values and pH 7.4). It's a 65l tank with honey gouramis, corydoras, tetras and two newly added male guppies. The guppies were added yesterday and over the past 24 hours, one has developed what looks like fin rot. It looks like a cut in the middle of the tail which has gradually been getting larger. The other guppy is ok as are my other fish.
http/s492.photobucket.com/albums/rr282/fionah88/?action=view&current=photo.jpg
http/s492.photobucket.com/albums/rr282/fionah88/?action=view&current=IMG_0108.jpg

 

[the duck]

While I have never had a fish with fin rot myself, this doesn't look like what I understand fin rot to look like. It appears that he is probably just stressed, is he being chased or anything else unusual in the tank you can think of?

 

[arobinson1984]

Its hard to tell from the pics. It may be that something has nipped the tail of the guppy.

If it is fin rot then the tail will quickly rot away usually over a day or two. Keep an eye on it and maybe increase your water changes a little, nice fresh water will promote faster growth and repair of the tail and water changes are usually more effective than most medications.

Becareful with melafix, I've found in the past that some fish dont take too well to it.

Andy