I wrote a paragraph or two just at the time Tony made updates to the system and lost the entry and forgot to return
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Aculeatus is diurnal and small egged.
Link should be fixed for Island Marine Life. Lynn has a variety of serpents, including the harlequin (Ken - SealifeInc - won't mind me suggesting you shop with Lynn as he is trying to work full time with
reef restoration projects and Lynn shares his facility). Avoid sea stars that are not either brittle or serpent or thorny and avoid green serpents. The Florida common star is not harmful to an octo (or visa versa) but is not a meat eater and will eventually starve with the lower lighting in an octopus tank. Even reef tanks are problematic for them and need to be estabished a long time before a common star will be able to find enough food to survive). Other starfish have starvation or aggression issues so keeping to the serpents and brittles is recommended.
If you are lucky, any polyps or leather you buy will be mounted on a small piece of some kind of substrate. If you are shopping locally, look for softies that are attached rather than loose. You will want to wedge the attached substrate into your existing rock so that the coral has water flowing around it (this helps for feeding) but not where you octo will maul it everytime it moves around. Generally speaking about 3/4 up the LR and toward an edge works well. Loose polyp mounting is better addressed by a reef forum and not suggested for your first softies but if you go that route reefcentral is a large community that is likely to have several methods for you to consider. Unless you are particularly graceful with super glue, I would avoid that method of attachment.
Depending upon the characteristics of your fake rock (is it porus, is it smooth, are there lots of grooves) it may or may not be an acceptable surface for corals. The surface and porocity matters less if you are using it as a base to support pre-mounted, non-encrusting corals like leathers. If you get a spreading encrusting coral the surface will make a difference. I guess the frustrating answer is, as usual, "it depends".
Yes, you have to feed the corals but there are different takes on this as well. Many corals feed on plankton that is hosted internally and needs light to grow but even these corals usually need meaty food. We feed our tanks 6 days a week with one day fasting. Many other people only feed once or twice a week. All of our tanks get a few squirts of frozen Cyclop-eeze and frozen mysis on feeding days (along with a small amount of liquid vitamins). You might cruise the different on-line stores, see what interests you and then look up the individual care criteria. Once you have a list and are armed with care knowledge, THEN go to your local pet store and see if they have any on your list. I would also make a list of Do No Buy's so that if you find something interesting you will know to avoid it. Additionally, most good aquarium stores have a well worn book with coral descriptions and care that you can reference while you shop.