The leavening goes out of it if it's around too long. We use a mix as it's consistent from person to person making it. We make it as we go, so there's never much left. We use Fry Crisp. There are several brands of batter mix on the market. I have even seen people use really thin pancake mix. What's nice about a mix is you can make as much or as little as you need, and you can mix it as you need it, so if you don't sell any fish, you don't mix any batter. Left to my own devices, I would cut out the beer and use water instead as I don't like the beer taste. It's my opionon only, and I'm sure I will be in the minority here, that beer competes with and masks the flavor of the seafood. It seems to me that beer batter never really gets crisp and gets soggy faster than batter made with water. I hate to think how many tons of fish I've batter fried in my lifetime. I have used mixes and secret recipes, with and without beer. Overall I prefer a mix made with water. You can always tweak a mix if you want and add whatever you want. Believe it or not, years ago everybody used to add yellow food color to their batter. I remember when Fry Crisp used to be sort of orange (from paprika, I think) now it's white. Be careful about adding salt. Salt will trash you fryer oil, and as expensive as it is now you want it to last as long as you can.
