Y'know, I've never measured accurately how much bleach I use. I just squirt some out of the carton into a round 1 litre container, then I fill up with hot water and give it a swirl around. I do use roughly the same amount every time but I judge it by eye. How unscientific!
I don't think it's anything like 10%, but I'm probably using a different type/strength/consistency of bleach. I use a general household thick bleach, and I'd reckon my bleach:water ratio is more like 1:150. But as long as you use hot water and rinse off thoroughly, I don't think it'll matter too much the exact strength of the solution. As long as it's strong enough to kill germs and rinsed off completely to prevent any residue remaining on the shells, I think you'd be fine...

I don't think it's anything like 10%, but I'm probably using a different type/strength/consistency of bleach. I use a general household thick bleach, and I'd reckon my bleach:water ratio is more like 1:150. But as long as you use hot water and rinse off thoroughly, I don't think it'll matter too much the exact strength of the solution. As long as it's strong enough to kill germs and rinsed off completely to prevent any residue remaining on the shells, I think you'd be fine...