Guppy Health Emergency Please Advise

[Freakonomist]

Hello,
My 60 gallon aquarium is stocked with 5 male fancy guppies. The fish have coexisted in amity for about three weeks. Three days ago, the smallest guppy began to harass (fin nipping, chasing) a considerably larger guppy. I'm in the process of aquascaping so I decided to wait until I introduced some hiding places before I resorted to isolating the bully. After adding plenty of decor including driftwood and live plants, the bullying has not abated. Upon observing some particularly viscous attempts to nip at the victim guppy, I isolated the bully guppy by placing him in a small plastic vessel that I perforated.
The victim guppy now spends most of his time laying on the substrate. His caudal fin is torn up and his slime coat has significantly diminished in its shine. Now another guppy seems to occasionally nip at the victim guppy though I'm really not quite sure if this guppy is aggressively attacking as the bully was . This guppy seems to just follow the victim guppy about without much contact but sometimes appears to finnip/headbutt.
Could the victim guppy be sick and the others attempting to kill off the host of an infectious disease? I know nothing of guppy defense mechanisms. 
I've noticed the victim guppy is considerably duller than the rest of the stock. Could my LFS have misidentified a female for a male? 
 
Thank you fishfourms community,
Freakonomist
 
 
 
 
 
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[Ny82]

How long has your tank been set up? 
Male guppies - if kept by themselves- tend to bicker. I have 5 males and they all pick on the endler. Not to the point of bullying him to almost death though. One of my males looks like a crowntail betta as he gets nipped by the dominant male.
Maybe there is another underlying issue with yours which is why I asked about your tank. Did you cycle it and what are your water stats please. 

 

[Freakonomist]

I take excellent care of my water. I cycled my tank for about 3 1/2 weeks before adding the stock. Both nitrite and nitrate are at zero. No ammonia. I do a 20% change every 5 days. 
I maintain my pH at 7.3. My tank has been up for a little over 6 weeks.
None of the other fish nip at one another. Have you noticed any fin damage on your guppies?
Thank you for your quick response Ny82,
Freakonomist
 

How long has your tank been set up? 
Male guppies - if kept by themselves- tend to bicker. I have 5 males and they all pick on the endler. Not to the point of bullying him to almost death though. One of my males looks like a crowntail betta as he gets nipped by the dominant male.
Maybe there is another underlying issue with yours which is why I asked about your tank. Did you cycle it and what are your water stats please. 

 

[Ny82]

That's good then. My cycle took ages, once the ammonia was finally down, it went through the nitrogen cycle and I lost a lot of fish. It could be your guppy is victim of stress just from the bullying. All my males have nipped tails from bickering with one another, it's normal male behaviour but like I say not to that extent. 

 

[Lillefishy]

Have you got a pic of the victim?
If it's much larger & dull in colour it could be a female, if so it will be harassed by the males wanting to mate with it

 

[Freakonomist]

That's good then. My cycle took ages, once the ammonia was finally down, it went through the nitrogen cycle and I lost a lot of fish. It could be your guppy is victim of stress just from the bullying. All my males have nipped tails from bickering with one another, it's normal male behaviour but like I say not to that extent. 

Right.... thank you. Any ideas? Could the injured guppy just be ill? 

Have you got a pic of the victim?
If it's much larger & dull in colour it could be a female, if so it will be harassed by the males wanting to mate with it

Select the second linked image for a picture of the ill and injured guppy. It was sold to me as a male and is somewhat brightly colored. 

 

[Ny82]

It's possible that he is ill and the others are therefore picking on him as he is weak. Is it the bluey coloured one with the red fins and tail? It's definitely male then and they are establishing the pecking order, he might be weak from being ill and is being bullied for it.  Just in case it's a spike since your cycle was done in just 3 1/2 weeks, have you checked the water? Nitrate should not be at 0-shake bottle 2 vigorously then take the reading again, it will show up.

 

[Freakonomist]

It's possible that he is ill and the others are therefore picking on him as he is weak. Is it the bluey coloured one with the red fins and tail? It's definitely male then and they are establishing the pecking order, he might be weak from being ill and is being bullied for it.  Just in case it's a spike since your cycle was done in just 3 1/2 weeks, have you checked the water? Nitrate should not be at 0-shake bottle 2 vigorously then take the reading again, it will show up.

I test both my nitrite and nitrate with a test strip and I can't make out any discoloration on the nitrite and nitrate readings. The other fish are just as happy and healthy as they have ever been. I'll test the water again right now. Could my frequent water changes be keeping the nitrate down? Or my live plants? Yes that's him. Why is it only he is being bullied? If all of this is in the name of social hierarchy why no other power struggles? None of this seems to add up aside from illness angle. Thank you very much for your help.  

 

[Ny82]

I have 1 male who is the boss of them all. They all fall into the pecking order, nobody challenges the alpha male. The endler is the bottom of the pack, he might bicker with the one above him but all in all alpha male chases everyone and keeps them in check. 
I haven't used the strips before. If you check it just now then that would be great thanks. The only other explanation is he is ill. 

 

[Freakonomist]

I have 1 male who is the boss of them all. They all fall into the pecking order, nobody challenges the alpha male. The endler is the bottom of the pack, he might bicker with the one above him but all in all alpha male chases everyone and keeps them in check. 
I haven't used the strips before. If you check it just now then that would be great thanks. The only other explanation is he is ill. 

I really haven't noticed any other bickering at all except maybe some fuss at feeding time.
My parameters:
NO2- : zero
NO3- :maybe some very slight discoloration on the tab. Maybe 10 ppm.
pH: 7.3
General hardness: 15 ppm
carbonate hardness: 50 ppm 
I haven't tested ammonia in about 2 days but at last test the reading was zero.