Have you ever boiled a pot of water dry and been left with white crusties in the bottom of the pot?
This sound like basically what is happening. You probably have a slow leak in or around your pump, as the water dries or evaporates the deposits are what is left. I would check the seal on the pump as this is the most likely culprit. As for the yellowing in the ozone tube, the ozone gas is oxidizing pollution in the air with it as it is on route to the hot tub leaving colored deposits in the tubing. This is completely normal, in a way this is how you can tell the ozone generator has been working. The colors deposited depend on the impurities in the air.
