I'll probably put a fang puffer in the 20l. It meets min req and long enough to give them adequate swimming room.
I'm temporarily trying to stay away from brackish and salt water puffers until I get more tanks and enough money to keep those types of puffers. Cleaning the tanks took me one hour for each. I used a lot of elbow grease :p
I just got another tank recently. Its a 6 gallon tank
I'm planning to rehome a group of red cherry shrimp population to this tank. If it starts over filling with shrimps, then I will feed the less colorful shrimp to my 2 south american puffers.