mechanical filters like your HOB are not needed in saltwater and in fact are in many ways a bad thing. they trap planktonic life that you want to stay in your sytstem and all the waste they trap just breaks down and turns into food for algea unless you want to be cleaning in every couple days. Most anemone need high light, and good flow. High light is an issue when it comes to keeping your tank from overheating and is more important in smaller tanks as they swing faster.
weather it fresh or saltwater all of the failure I have ever seen boiled down to the hobbiest not being properly edjucated and giving up when they are faced with their first failure. so dont give up a read, read, read!
You will hear the phrase " my tank crashed"...well unless it actually fell to the floor and broke, in MOST cases that just means the hobbiest was ignorant of the goings on of their system.