Right here is some info for you. But other people may say different so please bear all in mind!:
A good minimum tank size is US 5g (I have one in this size, he is absolutely fine). The 20 litres in the calculator at the top seems...fine!
They like quite warm temperatures I have mine at 26C, temp could range from 23-28c
They will get around an inch in length, live 5 or more years (very average on looking at websites)
The DP will not mind sand or gravel, whichever you would prefer. My large tank has gravel and my small sand, no difference at all.
They LOVE to explore the more planted and interesting objects in their the better, mine are a little lacking and plan to plant up more soon. It is nice to give them something like a coconut hut for hiding, though again depends on the puff and where they would like to make their own home!
Foodwise, bloodworm is a good main staple, you may need live to begin with depending what they have been brought up on and wean off. Frozen bloodworm is great, the blister packs will last absolutely ages, especially if cut the cubes into halves or thirds and thaw as need. Snails are good for them and their beaks and it may be good to get a small snail breeding tank/ critter keeper going. There is some debate as to whether DPs need snails, but I would like to promote snails, it can't hurt and helps to vary their diet.
Have also fed mine on daphnia and brineshrimp (live).
live packs of daphnia, brine shrimp and bloodworm are about 99p each, frozen blister packs about £2.50 ish.
hmmm...anything else...not sure, please ask and enjoy!
Oh it is hard to tell the sex of the species when they are juveniles, as they mature it will be easier and you will find out what you have. In general the males develop a dark stripe on their bellies (though this is also true of the dominant puff) and also can get blue wrinkles around the eyes.
EDIT: looking at the pinned topic at the top of the Oddball section, 5g recommended, 3g if keeping absolute crystal clear water, so you are fine!
