Dsc is right. Starfish belong in the ocean. Once the food source gets depleted they die and create more issues in the tank. I volunteered in a store- the amount of starfish that died weekly was sad...the mess they make is nasty! It looks like diatoms or possibly a brown cyano you have. I had it in my tank for the first 5 mnths on and off. I implemented the following: 1. Added an additional powerhead to get more flow to the lower level of tank 2. Clean out filter, intakes, pumps, ph monthly or more 3. Replace filter floss 1-2x a week 4. Rinse carbon bag at every water change and replace completely every month(unless its a product that lasts longer like chemipure) 5. Added more nassarius snails 6. Fed less 7. Vacuum sand bed lightly at waterchange day, use turkey baster on rocks. It worked.