Go through this checklist questionnaire...it may help you discover the nature of the problem. For help, go to the message board and let us know.
What is your pH?
Do you use salt?
What temperature is your Guppy tank?
Any sudden recent fluctuations of more than 4 degrees?
Any sudden changes in temperature or pH?
Has anything been done to the tank that is out of the ordinary? Such as changes in water changing practices or addition of new fish or plants, use of live food, new tank decorations?
Is there a possibility of any of the following being in contact with fish tank:
Aerosols, sprays paint fumes, tobacco, other fumes or chemicals, metal of any kind?
Any new piping or plumbing or mains work by the local water supply company (such as addition of chloramines)?
What is the size of the tank(s) involved and the stocking level?
What is your method(s) of filtration? How often do you make partial water changes? How often do you rinse the filter or change it?
What types of food do you feed and how often?
2. MORE DETAIL
When did the problem start?
How many fish are affected?
What action did you take?
What medications have you tried?
Fins: Split, ragged, or deteriorating? Clamped or pintail? White or dark edges?
Body: Bulges, spots, growths, discolouration, sliminess, worm-like parasites, swollen, protruding scales? Bleeding or red streaks on the body? Worms protruding from anus? Thin, emaciated? Spinal curvature?
Gills: Swollen, reddened? Is the fish gasping for air?
Eyes: Protruding, cloudy, missing?
Behaviour: Flashing or scratching on objects in the tank? Unnatural swimming, such as floating, looking intoxicated? Loss of appetite? Spits out food? Listless and inactive, resting on bottom? Gasping at surface of water? Rapid gill movement?