Mbu like hard ph 7+, and pea puffers like it soft 6-. Mbu are also large, dirty and predatory, while pea puffers need plant cover (never kept either.) Even if the mbu doesn't eat the peas, it would be needlessly difficult to care for them together. Just set up a 5-12g tank for pea puffers, it'll be easier and healthier for them.