Going to have to put on my sheepish face here. I thought this was the T8 setup thread, no the 20L one. My bad!
An average size male BP would be fine in a 20L for his entire lifetime - the footprint of a 20L is very similar to the most common sized tubs used in the business for grow-ups and males. An adult female, however, would likely need an upgrade as she reaches her full potential.
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