First, welcome to BYC.
Second, I am sorry to hear about your chicks.
If you still have that stuff in there, please remove it immediately and check the dosing instructions. It may or may not be that, but I'd remove it from the equation anyway.
Outside of that, I assume that they have chick feed (medicated or non-med), fresh water, and a heat lamp that's keeping them at the appropriate temp for their ages?
Are you using CEDAR shavings in their brooder?
In this situation, I would emergency-speed clean out their brooder, replace the shavings, wash their water and feed dispenser, put it all back, and make up a batch of Corid water.
Corid treats Coccidiosis, which young chicks are particularly vulnerable to. You can get it at your local feed store or
Tractor Supply. The dosing is as follows:
1.5 teaspoons (NO LESS) of the 20% powder per gallon of water
OR
2 teaspoons of the 9.6% liquid solution per gallon of water.
Make sure they have access to the Corid water ONLY for five to seven days.
Any more information you could give on your situation would be very appreciated.
MrsB