Oxbow pellets contain wheat and cane molasse. Tomato and carrot is a food with sugar. Are you sure that the mix pellets+these vegs are not the cause of the trouble? Why do wild animals have no bloat even eating the "dangerous" spring grass? 1/4 cup pellet is considered excessive nowadays; the new researches recommend not more than one TEA spoon...
Anyway the chemistry work just the same into us and into them: and when you need an abdomen ultrasound you are never allowed (at least here we have these rules) to eat wheat and sugar. But you can eat (alone) all the vegs you like... If I were you I would get rid of pellets and about calcium I would follow Guinea Lynx food list and calculator.
I adopted a piggie (months ago) who came home with some bladder issue and an alert for her being prone to calcium deposit. Her urine now is better than mine... no deposit, she does not drink at all (because maybe the vegs and fresh grass keep her body well hydrated), 3-4 pieces of pellets a day as a treat only, a lot of clear wee and a satisfied vet...
(a thing I don't like of industrial food: their labels never report the percentage of carbohydrates and harmful sugars...so strange... but you can get an idea when you sum 14% proteins+26% cellulose+ 8,5% cendres+ something else=? no good! definitely far from a natural diet for piggies... and I am reading on the label by Oxbow that they suggest 20g only a day, not more).
Sorry for this "sermon" but if most piggies (and humans!) have all the same issues, maybe some habit considered right is actually wrong... it can be a tomato, it can be a pellet, or maybe tomato+pellet!

I deleted pellets and my piggies have no gas, no deposit, nothing wrong, differently from another poor piggie I owned many years ago, who surely died thanks to the wrong diet approved by his savvy (and expensive) vets.