That is a really nice looking Malu.
I would scoop an area of sand nestled up against a rock or two, in an area where flow is moderate.
A 20g is kind of tough to keep params stable, not saying it can't be done, just harder.
They do require pretty stable params.
They do stay much smaller compared to crispa, the other sebae(I wish we would start calling them either crispa or malu to avoid confusion, such different species and demands)
good luck to you.