Hi mlinton!
well, a late welcome to the board.
Softies feeding.. it really depends on what kind. a lot of them are filter feeders, feeding off nutrients in the tank. many people feed their tank with phytoplankton a.k.a green algae water.
Xenias and anthelias.. i have never seen them actually "eat" anything. They are strictly filter feeders...
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green start polyps too, dont' "eat" anything really...
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Toadstool leathers feed off of micro stuff in the water
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Most zoanthids are filter feeders too, but I've seen those that will open up the "mouth" to eat
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Tree corals and colt corals, generally are filter feeders, but if the polyps are big enough to close up on certain foods, they will too.
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Whereas softies that look like they have a mouth (palythoa polyps):
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you can feed them with small food (shrimp, cyclopeez etc), and the polyps will close up.
These yellow polyps will do the same:
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When it comes to mushrooms and ricordias, some of them will close up on food to eat, some won't. Mushrooms spread like weeds so there's no need to feed!
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so pretty much softies w/ polyps can eat micro foods, or larger foods, depending on what they can fit into their "mouths". But feeding is almost unnecessary most of the time, since over feeding can cause lots of problems. Let me put it this way, if you don't feed them, they won't die, if you feed them, they grow faster (but may pollute your water faster too)
did i miss anything?