Looks like ringworm to me. They ALL need to be bathed in an antifungal shampoo such as a povidone iodine scrub or a betadine scrub, you can also use a chlorhexidine scrub too. You can find these at your local vet. Take one rat in and let them use the Wood's lamp on him/her, and see if the rat glows green. If so... It has a fungal infection and everyone needs to be treated. All cages need to be bleached and all accessories bleached/rinsed as well.

Dog food is for dogs and doesn't include everything rats need to be healthy and thrive. Find a feed store that sells Purina Products(call around), and have them order you some 50lb bags of Mazuri Rodent Block 6F or 9F. They are formulated for rats and mice and will be a much better food source. Dog food, especially crappy dog food, contains alot of by-products, artificial preservatives, "meals", and also contain alot of corn, which makes them feel full, but they aren't getting any nutritional value out of it. Most dog food is filled with fillers and junk. Not healthy for the rats, and not healthy for the snakes who eat them.