I have been selling SwimSpas for almost 20 years. I discovered this forum recently as we are always getting people asking us chemical issues, most are not our customers. I make this brief, there are 2 chemicals used in pools & spas, bromine and chlorine. Traditionally, bromine is used in spas and chlorine is used in pools. Pools use chlorine because of price and of course there a stabilizers for chlorine, meaning it will protect your chlorine from getting eaten up by sunlight. Sun will kill chlorine very fast if you do not have stabilizers in your pool, the same issue we found with swim spas (though not the same extent), but sunlight will quickly kill the chlorine in a swim spa in addition to the extra heat not normally found in a pool. I agree, keeping your total Alk balance is very important to the effectiveness of your chemistry.
Cheers, hope everyone enjoys their swim spas. Feel free to ask me anymore questions.