Maybe, maybe not. Probably not, I s'pose. You are now trying to get the 2 bacteria colonies bigger again. SInce you are getting DOuble Zeros after 24 hours, you should be having to dose every 24 hours, but not necessarily getting DOuble Zeros after 12, until the colonies have grown again. Once you're getting DOuble Zeros after 12 hours, check that the same thing happens again for a week, then you are cycled, and it's FISHY TIME!