Wow you guys are harsh!
I have a 30G display, so its a little larger than yours, but there's also a 30G sump behind it on the floor, so I've got about 50G total. If 24G is your
total water volume, then yes, it will be tough keeping stable parameters. What I did was buy a cheap cabinet at Office Depot, reinforced it with a frame made of cheap lumber from Home Depot. I put my my tank on top, and the sump in the bottom part. Works fine!
I run bare-bottom with Deltec APF600, almost 2000GPH of flow, and 150W 10K MH. I use B-Ionic for calcium/alk, but have a Deltect Ca reactor lying around if the time comes.
Its been running for about six months, and I have around 35 SPS frags in the tank right now. About eight are milles. They're growing nicely, but I'm not very colorful yet -- working on that.
WHY? I live in an apartment and I dont have room for a large tank. We're buying a house within a year, and by then I should have some small colonies ready for it instead of starting fresh with a bunch of silly little sticks.
So, dont let people get you too down. If 24G is the most system volume you can get, there are definitely SPS you can keep provided you give them the right conditions. People do it all the time.