The black spots look like scabs. Probably from light skirmishes and pecking order stuff.
It *could* be fowl pox, but it really doesn't look like it.
Either way, you don't need to do a thing unless you start seeing lethargy, not eating or drinking, hunching/puffing, bubbly eyes, runny beak, sneezing, wheezing, or gasping.
Have you wormed your flock lately? I recommend Valbazen liquid goat wormer.
MrsB
Have to agree with @MrsBrooke this looks like pecking. Unless you keep your chickens separated from one another completely, most will have peck/pick marks on their combs. Could be insect bites or Fowl Pox, but not nearly widespread enough to think it's pox.
FWIW Corid is not an antibiotic and is a very safe and gentle medication. It won't hurt and would be a good idea to treat them with it.
As suggested worming may be in order, but if you are worried about all the meds you have been giving, take some fecal samples to your vet for a fecal float test. This will give you confirmation of worms or not. I also agree Valbazen would be a good choice for de-worming.
Corid and Safeguard or Corid and Valbazen can be used at the same time... I have done it several times and neither of the drugs list each other under "drug interactions".
I would not put more than one medication in the water. What wormer were you going to use?
So what worms do you want to treat? Do you want to do it orally or in the water?
