Starting over

So -- a few months back all my chickens got sick. I tried for a while to save them but ended up having to cull the whole flock. Sad. Well we were at tractor supply yesterday and saw all the baby chicks and decided it was time I wanted to start over. I have been up early this morning bleaching and sanitizing everything...

My main worry is that we used out chick brooder as a chick "hospital" a few months ago. I have sprayed down with bleach, but is it still possible the new chicks can get sick from old bacteria? It was probably back in August or September, so it's been a while but I would hate to go through that again with little ones.

I haven't even started the major clean on the coop, I feel like I have a couple months for that...