Daphinia are a good food for helping with stomach probs.... As well as peas...
Remember what they'd get in the wild (not alot), i have a weekly fast day for all my fish, when they're lucky if they get half a pea, including my betta. I try and feed daphinia twice a week as well, no fishy food related problems (excluding overweight gourami; pleco+courgette+greedy gourami=fat fish) Dunno hope that helps.
Is your water acidic? Bare in mind that nutrient rich/poor waters (based on species) and incorrect PH (based on species) can lead to osmotic shock which is much the same as swimbladder.....