Valbazen is good, and dosage is 0.5 ml for a 4-6 pound chicken. Repeat that dose in 10 days. Fenbendazole (SafeGuard goat wormer, SG horse paste, PANACUR horse paste) dosage is 0.25 ml per pound given orally for 5 days. To treat just roundworms, give it once and again in 10 days. Each chicken must be dosed separately, and that cannbe done by grabbing them off the roost just before daylight, dosing them, and releasing them. There are a couple of wormers, such as Prohibit (levamisole) and Wormout gel that can be put into the water. Those are available online with dosages. Your most accurate dosage is to give the wormer orally. Be sure and shake the Valbazen or liquid SafeGuard well before withdrawing the dosage, since those are suspensions, and will settle out in water.