All sand, live rocks and corals were collected off the local reef here in the Philippines ( I am retired U.S. Navy and do nothing now but study the reefs, also known as goofing off in the tropics)
The ATS is now fully matured and when I think it is time to export some nutrients, I simply scrape off 1/3rd of the algae and rotate scrapings as needed. I used a piece of needle point cloth which is very stiff and rugged for the algae to grow on.
This system is virtually maintenance free and will do a partial water change if I feel like dragging home 5 gallons of ocean water, but so far all I've done in the last month is add top off water.
Just noticed these Tunicates within my tank today and am thrilled because they are notoriously hard or impossible to keep and if they have grown large enough for me to now see them, that tells me that my little ecosystem is on track
They are filter feeders much like sponges are. Oh, and that greyish area to the right of them, that is all sponge that has encrusted that entire section of the rock, hopefully it will start putting out "towers" which would look cool