you have to play around with it, watering top and bottom.
once u get it figured out u will have to add very little water from top.
but dont let top dry out.( or bottom either)

If your growing area is only 24" long then those lights almost have to be suitable because you
don't have a lot of alternatives. Short fluorescent tubes are relatively inefficient and these are
going to be borderline for growing lettuce, really only useful for a single row of plants right under
the ...

I would return them and get the 8'. Also, make sure you keep them on for a good 16 hours as these don't put out a lot of light.
Amanda