Is he rubbing on anything? It does look like ich to me. I wouldn't add any meds just yet, keep the water really clean and try to reduce stress. If he's still eating and not lathargic he's not that bad.
Have you ever treated Ich with heat and salt? You can slowly raise the temp of you tank up, over a few days, I believe to about 85 and this speeds up the life cycle of the ich. You can't kill it while it's in cyst form on your fish, you have to wait until the cyst bursts and they become free swiming.
While your raising the temp you're also slowly adding rock salt. Not table salt of course. Just plain old rock or aquarium salt. I buy my from the grocery store, it should be free from additives of any kind. Disolve the salt in some water and add slowly until you're up to a teaspoon of salt per gallon of water. Salt doesn't evorapate so when you do a water change only add back enough salt for how much water you took out of the tank.
A week like this is usually sufficient to kill off any ich, do some extra vacuming in both tanks as Ich lives in the gravel. Ich will also be present in your main tank (becuase it is just usually there) but most healthy fish are strong enough to fight it off which is why you're not seeing it in the other fish. The Rainbow is likely experiencing some additional stress... maybe the danio's are chasing him?
