I was thinking that it would be just the opposite

Hard to keep a culture going.
I believe it would not be possible or practical to grow Spirulina in a reef aquarium system. The nutrients needed for any single celled algae, including Spirulina are just not that abundant in a reef aquarium, or if they are abundant, the tank is in real trouble and will soon experience all the problems associated with high nutrient inputs.

Why do you ask? Are you looking for an easy way to feed single celled algae to your reef?