Is your parrot a white one or with unnatural colors as theres two different types of jellybean parrots. White one is just shortbodied pink convicts and another is dyed blood parrot which grow big.
Ok so if you are getting a true bp then a 30 gallon is pushing it. Although I believe a good minimum of 40 gallons is good for an adullt bp. If you buy him and grow him large then get a bigger tank I thnk you'd be ok. If I remember correctly, most larger cichlids take about a year to get to adult size.
If you are getting a true BP then 30gal would be minimum for a BP if you are talking about balloon convicts (jellybean parrot) then a 30gal would befine for a pair