Steve- I have the large CPR fuge on the back of the 46. They are definitely heavy (and some days it makes me nervous) but I've had mine on a 29 as well... and haven't had any issues. Honestly though, I'm less concerned about the tank supporting the weight than I am concerned with the "legs" that attach the fuge to the tank.
It definitely does a pretty good job of growing pods for me and honestly is probably pretty darn close to the total volume of the fuge on my 90 (once you figure the amount of volume that my skimmer and return take up in my 30L sump)
That said, overall I haven't been 100% pleased with the fuge. Here's a list of problems I've had that you should at least be aware of before you buy one:
1) The pump that came with it was junk and would continuously not start back up after a power outage or being unplugged. That small of a volume of water doesn't take long to stagnate.
2) If I use a pump that puts as much water through the fuge as I'd like I get a big time flushing sound out of the return (causing a microbubble problem). I've thought of ways to fix it, but they don't use a standard tube size so rigging some kind of durso-like return won't be easy.
3) When you turn the pump off, the fuge will siphon via the pump hose back into the display. This has never caused an overflow, but if you then do a water change out of the display, it will continue to siphon water out of the fuge until it's dry. This was easily fixed by drilling a very small hole toward the top of the pump tube, but was annoying nonetheless.
4) Make sure you get one with a black side toward the tank (or paint it before you set it up) because the fuge light will bleed into the main tank big time. If you want to run a reverse cycle or keep the fuge on all the time, the bleed over is annoying. I would argue that even with the black side it will be a little annoying, but if you can get the light mounted low enough, it's not a big deal.
Just wanted to let you know my experience... they work fairly well for what they are and are a much easier solution to your current problem than drilling the tank. They just have a few issues that I would have liked to have known about before I bought one.
).. I would recommend breaking it apart to drill it, though (much easier to do if you can get it on it's side and drill down rather than into it). I'd also recommend going as far down as possible for the drain line so that you can get as much durso in there as possible for the noise. I drilled a 75's back glass once, but only went 6 inches down from the top. I was able to fit a durso, but it wasn't the most functional. It was fine once it hit equilibrium, but needed some time to hit equilibrium... I've got diamond bits, too, so let me know what you want to do...
