I have 2 over my 3 foot 75 gallon tank. Seems tobe plenty of light but have not gotten around to testing PAR yet. Going to rent PAR meter from BRS to check it out
If you ahve the same 65 gallon standard tank as me. 2 should be more than enough unless you are planning on full SPS down low. I have a mixed tank. with sps up top, LPS in the middle and down low, and softies in the far out corners.