Welcome to BYC. What brand of wormer are you using? Putting the wormer in water or in feed can be difficult in knowing that they have taken the correct dosage. Putting something like Wazine (piperazine) in the water (30 ml or 1 ounce per gallon) is in the correct ratio supposedly if a chicken drinks a normal amount of water. They probably won't drink a whole gallon if there are only 6, but if you add that gallon to feed, they could either take too much or not enough. You also run the risk of them not eating it because they don't like the taste. That's why with only 6 chickens, I would use something like Valbazen, where you give each hen 1/2 ml orally with a syringe, and then repeat that dose in 10 days. That dosage is for a regular sized hen.