Good question!
I have just started keeping a pair myself, lovely little fish, really enjoying getting to know their characters.
I have them in a moderately planted tank with low rocks and thin pieces of wood, so plenty of cover and nooks and crannies to hide in.
The tank volume is 54L roughly 60x30x30 with an adjustable full width spray bar 3/5 pointing forwards, slightly towards the surface and 2/5 pointing down the back wall. Filter is stated to be 500lph.
The force from the spray bar isn’t quite enough to break the biofilm on the surface but there is constant flow around the tank as most of the plants are swaying gently.
I am planning to change to a stronger filter (same range but 700lph) in the next few days in order to better agitate the surface to break the biofilm, increase gas exchange and give a bit more flow for the Otos but am also concerned about how much flow is too much for these fish. I’ll let you know how I get on.
Right now they seem happy, they can hover without moving or drift with the current and have places to tuck out of the way. I guess the only real way to be sure is to try it out and observe any changes in their behaviour.
Hope this helps!