for a 2' wide tank I would for for 8-9" on the MH depending on the light spread from the reflectors, salt spray from the pumps and heat transfered to the water from the lights and 4" on the T5HO. If the T5HO are strictly supplemental then I might adjust that higher for better spread on the sunrise/sunset cycle and to give you more room when trying to stick your arm in the tank.
Mike