I've decided the ick is Isaac's ear is not mud. I think he has an ear infection. It's just in one ear, the left one. I keep cleaning it out and cleaning it out and there is just more and more of it. It's like a brownish, kinda thick discharge and occasionally I get a reddish streak or two, not bright red but more like rust-colored, which I think is blood. I am calling the vet tomorrow. He doesn't seem to be feeling bad at all, other than shaking his head vigorously at times. But I don't think it's likely to clear up on its own.
I do not mind taking Isaac to the vet. I want him to be healthy and get the medical care he needs. This is a really busy week for me but I will work it out. Hopefully we can get in tomorrow or the next day.