I believe anemones need good, direct food, and water that is as close to REAL seawater as is possible.
Anemones are strange critters. I've had some practical experience with keeping them however. First, I don't think that supplements are necessarily the answer as much as believed, but rather the quality and turn over of water. I don't mean gallons per hour, but rather NEW water replacing old water. Second, anemones feed via direct capture, by indirect "netting", which is more similar to how barnacles or mussels feed, and by sugar-producing microorganisms (zooxanthallee)within the anemone.
If you think about natural sea environments, water is relatively in infinite supply, and always "new" relative to a sedintary animal like an anemone. This natural water is constant, and balanced always, but there are not supplements. The anemone lives fine because of renewal water.
Now, since aquariums are finite, you primarily need to provide water that is as closely similar to real sea water as possible. This is where you need to actually do "trial an error" rather than research. Some animals will simply do better that others, despite the conditions of your tank.
I said I had practical experience....I did research in college with anemones. These were animnals from the coast of California. They had less light than anemones in the "wild". They even had filtered "cages" keeping them from filtering plankton and small food via their tentacles, thereby restricting "netting". I specifically was looking at simple growth, as measured by weight. In my research, I realized I had a unique system to work with. All my anemones were housed in a system that used sand-filtered sea water directly from the ocean. Also, 50% of my anemones had "expelled" their zooxanthallee algae because the anemone had been kept in the dark too long over a weekend. Therefore, they had NO commensilistic algae to produce sugar food for them, and light became a non-factor. What I found was my anemones did better with direct capture, or in my case, "hand feeding" fish parts to my anemones directly. Even the anemones without the algae thrived and grew more than anemones that had better light !!
Finally, I took some of my best anemones home, and kept them for over 3 years in my aquarium with tropical South Pacific fish. I used the same sand-flitered seawater in my aquarium as was in the lab. I only did water changes of 10-20% every 3 months! I fed the anemones with direct food, and sometimes brine shrimp. Remember, this was in '78....I had an undergravel filter, but no additional canister filter, no protein skimmer, no wet-dry. I NEVER gave any kind of supplement to them. I beleive it to be the water and food, and, probably that the anemones off the California coast are hardier. They are subject to greater shifts in salinity, heat, ammonia and siltation in tide pools.
Just to let you know, I also love anemones, but realized that most of the species available from the warm waters of tropical saltwater didn't do well in my systems. They would move all over the tank, and end up "shrinking" away to nothing.
Sorry for the ramble on, but I would gladly share what I know if you want to e-mail me your questions at: Fishfansea@aol.com