I agree - 40 breeders are beautiful tanks - bit on the small side, but great proportions.
I think the 2/3 cubes and similar sizes are very nice too, but they pose a problem if you wanted to keep tangs.
Assuming the average tang needs a straight-shot 6 feet to swim when fully grown, a 48x48x30 or 48x48x32 would give about 68 inches of space on its longest dimension (from corner to corner) - 51x51x34 would be the true size you'd need to provide 6 feet and stay within proportions. Those three sets of dimensions give volumes of 300, 320, and 385 gallons, respectively.
At that point, they become much more expensive to run - as you need to provide flow and lighting in such a tank. Adding volume via a sump gives you the benefit of not having to add extra lighting costs, extra flow costs, etc.
Further, the height is a problem in this tank because MH are the only lights that will give enough light to SPS kept near the bottom of the tank - so you're stuck either with MH lighting for a traditional aquascape, or you're stuck keeping your corals higher if you want to change your lighting.
One last note on the 40 breeder - how did you find the 72x27x24 dimensions? Going off the ratio of a 40 breeder (36x18x16), a 6 foot tank with those proportions would need to be 72x36x32, or 360 gallons.
I'd consider 20-30 minutes per day a good place to start as far as "reasonable". That includes checking everything out, making sure fish are healthy, feeding, cleaning glass, etc.
I would say that 40 breeders are my favorite of the small tanks, by far. It gives you some really nice options for aquascaping. My only problem with tanks of that proportion is that the volume goes up rapidly - about 105 gallons for a 4 foot tank, 210 gallons for a 5 foot tank, 360 gallons for a 6 foot tank, and an 8 foot tank at those proportions would be around 850 gallons. Rapidly increasing volume means rapidly increasing costs to run, due to flow and lighting - and tanks much over 24" deep are restricted in their lighting choices as well, meaning that a tank over 5 feet long with those proportions needs MH lighting.
As far as maintenance, I would think that the only things that take much longer on bigger than smaller tanks are water changes and glass cleaning, and the glass would probably only be noticeable going from tiny to huge - 4 to 6 feet is probably not much of a noticeable difference.
When my system is built, water changes shouldn't take me long at all, and they shouldn't cause any headaches either.
I will have two stacked tanks that are each 10% of the total system volume. The bottom one will be gravity-fed from the display, and water will be pumped back in via an external pump. The top one will have a water line feeding into it from a RODI unit, and it will have a few heaters and powerheads in it as well. Both tanks will have large floor drains - the top one draining to the bottom, bottom draining to outside.
Water changes will consist of filling the top tank, adding salt, letting sit 24 hours. Then, turn valve and shut off pump, so bottom tank is now cut off from the system. Drain it outside, drain in new saltwater from top tank, open ball valve, turn on pump, and 10% of the system's volume has been changed.
Much easier than lugging 5 gallon buckets around over and over again until everything's filled
Back to the main topic though - I agree on the thought of getting something off the bottom. From the tip of my middle finger to my shoulder is about 27 inches - so anything over 24 inches deep, maybe shallower, I'd better have something without sleeves on. I think 24-25" would be the maximum depth then, to allow me to safely reach the bottom of the tank without being submerged.
I don't imagine myself needing to reach the bottom all too often - but in the event that I need to, 24-25" depth will allow me to without donning a mask and snorkel
Drew
