A reef tank will a) cost more, b) take more patience, c) cost more, d) take more time to maintain, e) cost more, f) limit the types of critters (fish or otherwise), g) cost more, h) take more patience, and i) cost more....
Ok, maybe not THAT bad, but you will be limited again, not only by what size can fit, but the quantity will go down compared to a FOWLR (fish only with live rock) setup, and the choices of coral friendly fish is reduced.
One of, if not THE, biggest expense of the reef tank is lighting. As if it wasn't expensive enough.
Agree as well on the 75 gallon. A longer tank is better than a taller one. Good thing that the "longer" tank is much more common than a tall.
Either way, you are basically going to start with a FOWLR tank, just with limited fish choices and making sure that it is a little "under-stocked" in numbers. Then, a year or more after you add your first fish, you can look at adding corals. I tried my hand at corals for a while, and they were really picky about where they were in the tank, so I gave them away, and kept it just fish and inverts.
We also had a dedicated seahorse tank too. Talk about a pain in the butt. Those stinking things are so sensitive. I don't care how much experience you have, they are hard to keep healthy. One parameter is off the tiniest bit, and they want to die. Never again will we have seahorses. I would love to have a saltwater tank again. We had an accident with our tank a number of years ago, and I just didn't have the desire to start over, plus we lost thousands of dollars in fish and such.
Oddly enough, the programmable thermostat in our house malfunctioned over a weekend in April where we had the heat running just a little due to cold nights still. Anyway, the house thermostat put itself into a "heat - on" mode for at least a couple of days. We got home from being out of town, and the thermometer in the tank was off the scale, we had another thermometer in the house (a cooking one) that was in a drawer, and it was showing over 150F in the house!!! Needless to say, the fish were cooked... Our cats managed to get into the basement where it was a little cooler, or they would have been dead too. They were very lethargic and acted sick. We opened all of the windows/doors to try to cool it down, but the damage was done. The live rock and live sand survived, as did pretty much all of those nassarius snails I mentioned earlier, but our cleaner shrimps (cool looking and helpful critters), fish, and other small inverts were quite dead.
For anyone wondering, no we didn't get anything from our insurance or from the manufacturer of the thermostat. They had a disclaimer in their warranty that protected them from animal injury or death.
I kept the tank running without any fish for about a year before the sad realization came that I needed to sell everything and move on.
If I had it to do all over again, I would look at going with a 150 gallon tank. FOWLR again just because it was simpler. Then again, the length of the 150 gallon usually means specialized (read: "more expensive") lighting over something like a 125 gallon.
Just me. I didn't believe it when I had my 75 gallon. I originally was wanting a 50 gallon and got "talked into" a 75 gallon and was told that I would want something even bigger. It was true, but that 75 gallon was still a really nice size.
