The snow is calcium precipitation. It won't harm anything but if you notice clumping in/on the sanded during your next water change you should vacuum it. 1 & 2's or A & B's are meant to be dosed somewhat together (not at the exact same time). There is a balance between alkalinity and calcium that is required to maintain them in solution. When that balance is off (one is overdosed), the end result is precipitation. Further, magnesium is the final component that technically keeps them both in check with each other.
Your tank is fine but you should not dose anything without testing (maybe you did?). Also, I would be shocked if you actually needed to dose anything in a tank that size as long as you are doing regular water changes. Maybe a little alk and mag once and a while but unless your salt mix runs very low on calcium, I doubt you will even need it. Dosing anything also assumes you have animals in the tank that will uptake these elements. A bubble tip or LTA will not, at any rate to be concerned with. The few stony corals you could fit in the tank would also be hard pressed to deprive the system on a regular basis. I suggest that you do a water change and test your parameters about a day later and every couple days for the rest of the week. That will allow you to see any trends and you will know when and how much to dose (again, I don't expect you will need to).
A 10 gallon is a difficult tank for a hosting anemone. Not saying it cannot be done but the nem will eventually outgrow the tank and it leaves very little "wandering room" to stay out of powerheads and other equipment.