Guppies also look pretty lean and skinny, makes me wonder if they might have internal parasites too.
OP, would you please copy/paste the template below then fill in the answers please? The more info you can give us, the better the chances that we can give solid advice.
Also
@Colin_T is great with diseases/parasites, and
@emeraldking is a livebearer expert. Hopefully they can help.
Tank size:
pH:
ammonia:
nitrite:
nitrate:
kH:
gH:
tank temp:
Fish Symptoms (include full description including lesion, color, location, fish behavior):
Volume and Frequency of water changes:
Chemical Additives or Media in your tank:
Tank inhabitants:
Recent additions to your tank (living or decoration):
Exposure to chemicals:
Digital photo (include if possible):