sps is very easy to keep actually. It's getting the tank ready for them that's hard lol. The real answer is that it depends on the specific coral. There are differences in requirements between different sps. The big keys are very clean water, good lighting, big random flow, and stability of your parameters. It's not too hard to get the tank to the point where you can keep sps and get them growing. It's quite a bit harder to get them to color up properly. Don't worry about too much flow. More is better. you want a lot and you want it as random as you can get it. I'm runing 2 Vortech MP40's and a Maxijet 1200 in addition to the return flow in a 90 gallong. The vortechs are both nearly maxxed out. The MP40's push about 3,000gph so I have a good bit of flow going. Stability of your parameters is key, especially alk. If you have alk swings, even small ones, your sps won't like it very much. I'm running a CA reactor and auto topoff unit for stability. Personally I wouldn't buy anything other than a Geo CA reactor. Their design is better than any other I've seen. That has stabilized my alk, ca, mag, ph, and other params I can't even measure. I add kalk to my topoff water in addition to running the CA reactor. kalk won't do much to boost your ca but it will help stabilize alk and ph. You'll want nitrates and phosphates at 0 or as close as you can get it. I like deep sand beds for nitrate control and I run rowaphos and carbon constantly to keep p04 at 0. I change the rowaphos every 3 weeks. Any trace of nitrates and po4 and you'll start losing colors and start seeing issues with slow growth and recession. Did I mention stable alk? That's one of the most important things. Took me a while to get everything in balance with alk, ca, mag, and other params. I was able to keep sps and get growth but until I got my alk stable I wasn't getting much color out of them. Keeping sps may be the most expensive option for a reef tank. Whenever I've skimped on the price I didn't get as good results. Having a good protein skimmer helps a lot too. Upgrading to an Alpha 250 was one of the best things I did. My water became much cleaner and my corals really showed a difference. Did I mention stable alk?