These are probably too big for most aquascape scenarios, but I appreciate the Gwapa folks. Anyhow, two plain old green Severum, about 1 1/2 in long, body maybe 30% bigger than a quarter. The larger one does chase the smaller one kinda relentlessly, at least in my little 6 gal temporary tank. these are $12 - $15 size at a Pet Store.
Petco has their $1/ gal sale on again, by the way> 10, 20, 20 tall and i think 29 gals.