With the flat rate shipping on food from them, I tend to order a year's supply at a time to get the most out of the shipping cost as I can. I also see if anyone locally wants to order any at the same time to cut their shipping costs.
I'm surprised your clownfish won't eat it. All the clownfish I have will eat any type of fish food I throw in the tank. Give it a little time, and perhaps try mixing some of the mysis shrimp in with the food you were feeding them previously. If that doesn't work, you may want to look into a food additive, such as Selcon, to help entice them into eating the mysis.