You will need to either put in some dead krill, shrimp, or something that will decompose. I have even heard of actually pouring in a cup of your own pee??? I wouldn't recommend a damsel cause they are just a pain.
all you need is a raw ucooked shimp, but keep in mind that if you ever want to add lr it has to be slowlly (few lbs at a time)or you will encounter a ammonia crisis and maybe a small re-cycle.