I am still a newbie, as my tank is only 8 months old. I have a 75g with 4 360we. I don't know if I need them or not. I have one acro and it is growing like mad. So is everything else, with the possible exception of my two gonipora's which, if they are growing its very very slow. My electric green birds nest as exploded, my acan lord also budding off lots of new heads. And of course, what no one tells you when you start (all my zenieas are now a problem, they are growing everywhere and I am now in the business of yanking them out). The pulsing zenias are more or less easy to pinch and yank. The regular zenia is a big fat problem as it tends to encircle and strangle my zoas. Its become a labor of love to go in with forceps and try to untangle the zenia strangler arms from around the zoas than then pull them out. But what is the whole thing if not a labor of love?
The star polyps are a whole different problem as they seem to engulf zoas, I have an ongoing battle between a bunch of vampire zoas which are being overrun by the star polyps expanding base. As near as I can tell the zoas are trying to extend out beyond the engulfing polyp base. Where it was not to late I have now inserted small plexiglass walls to keep the stars from overrunning my purple haze and my pink gonipora etc.
Did not originally imagine there could be a problem of invasive coral attackers! Knowing what I know now, I would never have put any zenias or polyps in the tank to begin with. But maybe I would not have listened to anyone who told me that to much growth would be a problem.?
But back to the main point, Light, I do have a pretty good sized clam going into his 4th week and he seems to be doing fine under the 4x 360we.
So while I can't say that you need 4x 360we on a 75 gallon tank , I can say that my 75 g tank is promoting growth growth and more growth.