Sick Guppie? Should I Euthanize?

[ArronP]

Among my community tank I have 6 yellow guppies.  All are fine except one which floats at the surface... and has been doing so for about 48 hours.  It's very lethargic, but will move for food or when provoked.  Here are my water specs.
 
Ammonia 0
pH 7.2
Nitrite 0
Nitrate 30-40
78 F
 
It shows no outward signs of trouble (aside from the floating).  If you need any further information let me know.  If I need to remove it, I'd like to do so quickly as to prevent any damage to the rest of my community. 
 
Thanks!

 

[Betta_Shark5678]

In my experience guppies are very sensitive to high nitrates, yours might be too high for them.  I don't think you should euthanize, because if it's just high nitrates it won't matter if you euthanize this fish, the other fish will get sick, too.
 
I had ten guppies, my nitrates were staying at about 30-40, same as yours, and they started dying off with no symptoms other than being slightly lethargic.  I was injured, and my nitrates eventually spiked to 80.  I did daily water changes for a while to bring my nitrates down to 20, but all the guppies died The only other fish to die was a 6 year old golden gourami, who had been very stressed in the 6-8 months before his death.  So try a few water changes to bring the nitrates down and see if that helps!