If you’re intentions are sterilizing it and removing organics then bleach will do the trick. Some aren’t comfortable using acid. It’s also not any better than bleach anyways. I know you said you don’t want to use it, but it’s really easy to do. There’s details that can found right here. A ratio of about 1:10 will do the trick. Power washer will remove a lot of stuff also. Vinegar soaking is an option also. Never tried that though. You could always just scrub of with a stiff nylon brush using tank water if you want to preserve beneficial bacteria and such. Just don’t let it dry out. Peroxide also works well for algae scrubbing.
Whatever you do DO NOT boil it!!!!! Term cooking rock is often misinterpreted, as people think that you literally need to boil and cook rocks. Bleach is easiest and safest way of killing everything on and in the rock to start over again with clean slate. If you dont know what you are doing with acid, do not use it! It is dangerous and can cause you many issues in a second if you arent careful. Also acid physically destroys layer of rock, so you loose about 10-20% of it, depending on how strong of acid mixture you use, and how long rocks are in the mixture for.