How can I remove sealer from grout so I can clean the grout?

My DH sealed all the wall tile grout -- which was clean -- and then did the floor. But the floor wasn't clean and the grout has whitish patches on it. At any rate, is there a way to clean off the sealer so I can clean the grout first? He doesn't care about it, but the grout is charcoal grey so the patchy white stains under the sealer look awful.

He used something called "AquaMix Gold"

Also, he said the sealer is supposed to make the grout waterproof, but I read the bottle and it says it provides moisture vapor transmission and maximum stain protection. So that makes it doubly dumb to put over grout that is already not clean. So annoyed, it has cured for about a week. I tried to scrub it off with dish soap/water/vinegar mixture but I don't think it was effective :-(