It takes about a year, sometimes 18months, for a reef system to truly stabilize. Anemone's are very touchy to changes in water conditions, and if you're fairly new to reef tanks, you're bound to make a few little mistakes in the first few months. The fish will tolerate these little bumps in the road, but your $40 anemone may not.
Even if you don't make mistakes, the tank will still have to stabilize for at least 6 months before you'll have good odds of keeping the anemone thriving.
Also, if you think you need an anemone for your clowns, you're wrong. They do fine in captivity without one...and a lot of people have found that tank raised clowns will not bond with an anemone...the instinct gets bred out of them.