That looks right except you have too much lettuce. In that cup, you only need one small piece. IMO it's easier to make "green water" - algae which is food for micro organisms. But I think it has to be set out side, in the open, to work.
TBH I've never really succeeded culturing anything with dead veggies. But It does work if I just let it age out side until the water clears. I can't see anything moving in the water, but fry seem to thrive in them..... I use big tubs - my breeding tubs.