I order live salt water shrimp, about a hundred per horse and toss them in the system. Depending on the size tank and horse you have would depend on the number you should do.
I get them from seawaterexpress.com
If I'm gone for more then 5 days, I have someone come over who know about aquariums to check things out, fill up the top off unit, clean the pump intake in the sump, do a water change, and add more live feeder shrimp.