I would take the wormer back that
TSC sold you. There are much better products to use. Those are maggots, and you need to look over each chicken around the vents to see if there is poop built up or an injury. Remove poops, and keep vents clean.
Coccidiosis, worms, and enteritis can cause bloody mucus in the poop. Try to find out if there are maggots outside or they are comming from inside.
Do not worm until you figure out the maggot issue. If you need to worm them at some point, get SafeGuard Liquid Goat Wormer and a syringe. Give each chicken 1/4 ml per pound, and repeat it in 10 days. Or you can use Valbazen, and we can bive dosage.
For coccidiosis, get Corid at
TSC. Dosage is 2 tsp of the liquid per gallon of water for 5 days, and make fresh daily. After completion of Corid give vitamins for poultry for several days. Also, make sure that the maggots are not an issue first.