The only reason I stated safeguard over ivermectin is cost, safeguard is cheaper here where I live. Ivermectin has an advantage over safeguard in that it kills most lice/mites on chickens....that's basically the only difference. Your choice which you want to use, they are both excellent wormers. Just worm them once since you've already used wazine. The worm larva will be killed by either wormer. Keep in mind these are poisons you're giving your chickens to eradicate internal parasites and both do their job well. I didnt know the ages of your chickens. When one of your hens lays her first egg, switch from grower to layer crumbles...that's how I did it and never had any problems. Are they all the same age? And do you know what breed they are? Some breeds lay later than others. Keep asking questions, it's the best way to learn and if I dont know the answers, someone else will jump in and answer them.