Everyone knows that it's recommended to replace the toothbrush every 3 months, but I'm not sure I know anyone who actually does that. The toothbrushes are of such high quality now that they can live much longer than that IF you clean them well (and don't chew on them). It is not enough to just rinse them thoroughly after use. This is how I "deep clean" ours.
There's going to be some fizzing. All the yucky stuff that was on the brush will fall off. Rinse. Enjoy your clean brush.