a 20L should be large enough certaintly for a few years. at worst you may need to upgrade to a 40 breeder for the extra width of the tank. they are fun sausages of sassyness when fully grown. friend had one for about 6yrs I don't think it got more then 10".. side note.. as with most spiney eels. avoid course substrate, non-silica based sand (pool filter sand seems to be a prefered one) or bare bottom with hiding spots that are non-course. I prerfer PVC for my fire eels and TT and though not very natural looking, very easy to clean, and will not harm your fish.