Actually BER is a physiologic problem. It is a relative calcium deficiency due to problems with uptake of calcium from the soil and transporting it to the leaves on top. The calcium is taken from the fruit to keep the plant going.
Some people do add calcium when planting tomatoes as a hedge against BER, but even if the soil was rife with calcium the BER could still happen because the real problem is getting regular water to the different parts of the plant.
Tomatoes are heavy feeders. They need regular feedings of fertilizer and they need regular watering.
I did not have problems growing tomatoes in SIPS because the reservoir always has water so the soil never dries out. I do give my tomatoes in pots some balanced fertilizer that contains micros. It does contain potash of magnesium but apparently the potash is too small to count in the analysis. Still I have not had any problems with BER in SIPS or in my regular 18 gallon tomato pots as long as the pots have been watered daily and watered twice a day on hot and windy days. I mulch with white plastic, basically I cut the bag that contains the potting soil and fit it in the pot with the white side up. The plastic mulch cuts down on weeds and helps to keep the soil moist. The pot is large but once in a while I do catch the tomato roots going into the ground. Foliar calcium is +-, the real solution is to keep your tomatoes evenly moist and don't let them wilt. That means maybe watering and misting more often, mulching or if you live somewhere very hot providing some shade. It also helps in a hot climate to choose heat resistant tomatoes. They don't get BER as easily.
I don't like to add calcium to an acid loving plant. My water may contain some calcium and magnesium naturally. 5.93ppm Calcium which isn't very much. The potting soil probably has some lime added to it since most of them do but don't always disclose how much to "balance pH". I just don't add any more to the pot. In fact I added lime to my garden for the first time in years to keep the pH in my home garden from going lower than 6.0. Adding lime or gypsum won't hurt unless your soil is already alkaline, it just might not really help.
http://www.kellysolutions.com/erenewals ... _00_AM.pdf
Happy gardening in Hawaii. Gardens are where people grow.