Well, thom would know more about current in a 20G tall.. but i think 2 koralia nanos or 2 koralia 1's would be sufficient for current.
Well, i sold the 55G... and kept the 10G. So that's most likely going to be the next SW
tank if i can't find a nicer tank for cheap(round 20-30$). I'm also going small because of price lol. Couldn't afford to keep the 55G running on my non-existent salary. However, i like nanos more than i do the larger tanks.. so yeah the 55G would have never worked out for me in the long run. I will however admit that when i get older and i have my own place with a stable job, i will most likely buy a large tank(over 100G).