[fkshiu]

Everything kwirky said about T5s is correct. Unfortunately, the footprint of your 46 gallon bowfront presents a lot of problems. I had the same tank and I could only fit the 4x39W Teklight over it because the tank is too narrow (front to back) for any other T5 unit. The only way you could get a 6-bulb t5 unit over the tank is suspending it from the ceiling and even then you'll be lighting your floor as much as the tank.

The other option is to get a t5 unit without individual reflectors because you can smoosh more bulbs together, but that would defeat the purpose of going t5s in first place.

So if you do go with the 4x39W Teklight you will lose quite a bit of light compared to 250W MH. I kept LPS fine in my tank, but never tried clams or SPS.