Before using meds, try feeding partially boiled, shelled peas. Your guppies may simply be constipated.
I've never used parasite clear. Check if the med has methylene blue in it. If it does, it will permanently stain the tank silicone and some tank decorations. If you decide to use meds, it would be best to do so in a hospital tank - a 5 gal
bucket or rubbermaid container would do for guppies.