20 gallon is good, 29 preffered but a 10 will get the job done, just look out for aggression. And that 33 sounds great for breeding cons because if it is low it must be pretty long.
ive tried to breed cons in a 10 gallon with 2 pairs which soon broke into a fight killing one pair. they are 2 aggresive towards each other during breeding and should be kept in anything above 25 gallons.