Basic principles can do a lot:
Provide plenty of space, keep things reasonably clean and definitely dry (even outdoors, arrange drainage and/or plants to keep the animals out of the mud.)
Keep clean, fresh water available to the animals, and provide the right amount of the right kind of food (animals are more likely to have health problems if they are are starving, or obese, or eating food that is badly wrong for their needs.)
Be very careful about bringing home new animals, because they might have diseases or parasites as well.
Consider culling animals that are sick, rather than treating them. This keeps them from suffering (because now they are dead), keep them from spreading the disease to others, and usually means that you remove the animals with weak immune systems (they got sick) so the only ones you have left are the ones with stronger immune systems.
Corid treats coccidiosis. If the diarrhea is not caused by coccidiosis, then Corid will not help. Many other things can also cause diarrhea, and each one needs treating differently. (Example: chicks are more prone to diarrhea when their brooder is too hot, and fixing the brooder temperature will fix that kind of diarrhea-- but will not help against coccidiosis or any kind of bacteria.)
Yes, keeping things clean can make a big difference.