I always thought Valbazen also killed tapeworms? Is this not accurate?Please read posts #2 & #4 in this link, they will help you.
https://www.backyardchickens.com/threads/worms-in-chicken-poop.1575508/#post-26765905
For tapeworms, you need to use Equimax or Zimectrin Gold to kill the tapeworms. Only dose the birds that are excreting the segments that you see in feces. It's possible that only one or two birds have tapeworms. The moving segments in feces contain eggs. The segments work their way onto and into the soil where they release the eggs. The eggs are eaten by insects. Chickens eat the infected insect and the chicken becomes infected, not all insects will be tapeworm infected however.
You're not going to see gapeworms in feces since they are attached to the trachea. Their eggs can be detected in feces under a microscope.
I doubt your birds have gapeworm, you'd know it if you saw what they do to chickens.
Since you have alot of chickens, buy Valbazen. It will last you, and you only have to dose each chicken twice. The initial dosing, and another dosing 10-14 days later and you're done. It will eliminate every type of roundworm that a chicken can get.
I recommend setting up a regular worming schedule. I worm monthly due to our warm wet/moist soil most of the time. Perhaps you can worm your birds every 3 or 4 months or however you see fit since there will be worm eggs in the soil waiting to be picked up by your birds. Take a look at the poultry large roundworm lifecycle on the internet and you'll get a good idea how often you should worm your chickens.
We worm our dog monthly per our vet. Same thing, dogs easily pick up worms and need to be wormed as well.