hey cheeky, ive got a 300 gallon also, that i got up about a month ago, although mine is 96 long, 30 wide, and 24 tall, i used a barracuda for my closed loop it has 5 returns across the back of the tank between my two overflows, and just that one pump moves a ton of water, so much to where it will curl up thr front wall and across the top if i dont have them aimed right, and i use a dart for my return, i had an iwaki 70 for the return in the beginning but it was really noisy. i feed my refugium off of one of my downs and it works great. as far as plumbing the only 90's in my closed loop are where the plumbing goes directly into the tank, i found a pvc manifold which had 1.5 inch in and 5 1 inch outs, which i think made all the difference in the presure for my closed loop, and i plumbed it with flexible pvc. check out the website flexpvc. com , they have a bunch of cool fittings that i couldnt find localy anywhere, even true pvc Y's.