They would be fine in that and can be brought onto pellets. If you have good surface planting you could do 2, just make sure they have calm spots to chill out.I have adored butterfly fish for a while. How would they do in a 45 gallon? Just one with some bottom dweller to compliment? Do they eat pellet?
You can do some mid/ bottom fish like loaches or non-nippy medium fish like some rosey barbs or similar