Hi,
Thanks for your inquiry. Four 55W bulbs on a 75 gallon tank will be sufficient to keep soft corals, mushroom, polyps and many of the LPS coral. However, it will not be enough for SPS corals (including acroporas), clams or anemones.
For the latter, you will want more intense lighting. Such as four 96W PC bulbs, or some sort of metal halide lighting.
By changing to 10K bulbs, you are simply changing the color of the bulbs, the intensity will not change very much at all.
Please do not hesitate to contact us if you have any further questions.
Sincerely,
Joseph
Marine Depot Customer Service