That looks like cecal coccidiosis to me. The liquid dose is 2.5 ml per quart for 5 days, then 1/4 that for 7-14 days. Giving a couple of drops was a very good idea and exactly what I would have done.
The powder dose is no less than 1.5 teaspoons per gallon for 5 days, then 1/3 teaspoon per gallon for 7-14 days.
Since you ave chicks, you're probably using a quart size waterer, so I ould recommend using 1/2 teaspoon per quart for 5 days, then 1/8 teaspoon for 7-14 day. It's a just little more...