i had a 220 on my 55 with anemones. i think 75 are just wider not taller. so i think u can keep them, but let me tell u i put on 2x65 plus the 4x55 and wow what a difference it made. so i would look for a 6x55 pc i saw one for like 325. on . the lfs has 4x65 on a 75 for a sell tank and its ok but the front is not as light as the back so u have to place corals with the lights. i would go 6x55. i love it.