I would try to increase your water temp first, if that doesn't work Rid Ich+ always does. I just try to fight it off without meds first. Good luck and let us know how things are going.
idk about guppies but a lot of fish you can get away with, if raising the temp doesnt work, leave the temp up until white specs are all gone and add AQUARIUM salt
You can google Ick and pretty much its little white spots IMO and they are on the body and eventually get in the water itself and rocks. Turning it up in temp is good and be sure to watch your fish and make sure they stay good with breathing and etc.. and arnt cooking.