Anthias are difficult to establish in aquariums and you want a coral tank with lots of plankton for them. They also need to be in groups of 8 or more. One male with have a territory around 3-4 feet square and will have a number of females living in it. If you want Anthias, wait until the tank has been running for at least 6 months and has a lot of live rock, coral and plankton.
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Amphiprion percula and ocellaris look very similar but the ocellaris are a lot cheaper if you can get them. They are essentially the same fish but the ocellaris comes from the Indian Ocean (west and north coast of Australia and into Indonesia), and the percula comes from the Pacific Ocean (east coast of Australia and New Guinea).
All anemonefish (Amphiprion percula and occellaris) live in pairs, or groups consisting of an adult pair and a group of smaller fish that are neither male nor female. The adult pair keep the others in their place by bullying them. In an aquarium you should just keep 1 pr. The females are usually bigger than the males. If you can't find a bonded pr, buy 2 fish from a group and try to get the biggest and smallest one from the group. The biggest will bully the smaller one for a week while it becomes female, and the smaller one will turn into a male. Then you will have a bonded pr.
You don't need an anemone for the fish but they do like to have one. If you do get an anemone, add it to the tank before you add corals. Let the anemone settle in for a month before adding corals. Anemones sometimes wander around before settling down and they can fight with corals. Allowing the anemone a month or so to settle down normally prevents any fights.
If you have anemones in an aquarium with a power filter, put a sponge on the intake of the power filter to stop the anemone being sucked in.
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Fairy wrasses can be difficult to feed and do best in well established tanks with lots of live rock, plankton and macro algae (Caulerpa and Halimeda species). They live in groups with a male ruling a harem of females. Try to keep at least 4 of them in the tank and only 1 male per species. Most of the males are much more colourful than females.
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Bangaii cardinalfish live in groups among the spines of the black long spined sea urchin. You don't have to keep them in a group but they seem happier in groups in large tanks. A group will also let the males and females choose their breeding partners. When they breed, the males incubate the eggs in a buccal pouch in their bottom jaw.
Sea urchins (especially the long spined varieties) are a pain in the finger (you thought I was going to say bottom). They chew on cables and silicon when there is no algae to eat. You don't need them for the Bangaii cardinalfish and I don't recommend them for aquariums. They also have a tendency to hide behind rocks and you often get stabbed by them when cleaning the tank. The spines are brittle and have small barbs that make it hard to remove bits that break off in your fingers. If you have to have a sea urchin in the tank, get a short spined variety, they are much easier to handle.
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Scooter blennies and Mandarin fish are not the easiest to keep, They need live rock, macro algae and plankton. If you plan on getting these types of fish, make sure the tank has been running for at least 6 months and there is lots of live rock with creepy crawlies on it.
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Banded coral shrimp are highly territorial towards other shrimp including their own kind. If you can find a bonded pr, they will be ok. But they have to choose their partners and if a shop says just grab any 2 shrimp, don't do it. The pr of banded coral shrimp must be caught together in the wild, and live together at the shop. If you can't find a pr, get one and leave it at that.
If you want a group of shrimp, get Lysmata wurdemanni (peppermint shrimp). These can be kept together in groups and will breed in an aquarium.
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Hermit crabs come in a range of sizes and the smaller species usually do better in aquariums. That is to say they are less destructive in an aquarium than the bigger ones who regularly push over rocks. All crabs (hermit and normal) will push over rocks in the aquarium so check live rock for crabs before adding it to the tank. Most hitch hiker crabs are tiny (the size of your little fingernail) but can grow into 3-4 inch+ nocturnal predators that eat anything they catch and rearrange the rocks at night.
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Duncan corals and green star polyps are fine and usually do well in aquariums.
Purple branching hammer soft coral are actually large polyp stony corals that have sweeper tentacles they send out at night to kill nearby corals. Do not have these near any other corals or anemones. Keep them at least 12 inches away from other corals and anemones.
Brain corals also have sweeper tentacles they put out at night. Keep them away from other corals too.
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Protein skimmers can be helpful but also a problem. They remove protein and help keep the water cleaner for longer so that is good. However, they also remove plankton and that is bad for coral tanks or if you have fish that need plankton.
I tried using external canister filters on coral tanks (I used a Fluval 303 years ago) but found the corals didn't do that well. I tried tickle filters and they were good but painful to set up. Eventually I went for a small internal power filter or an air operated sponge filter, lots of live rock and lots of Caulerpa. The power/ sponge filter was more of a backup if I fed the fish heavily. The Caulerpa (macro algae) and live rock did most of the filtering and also provided habitat for numerous creatures to breed. A lot of these became food for the fish and corals in the tank.
If you do use an external canister filter, don't use the fine polishing pads that come with some brands. Just use ceramic beads/ noodles and a sponge. Clean the filter each month by washing the filter media in a bucket of tank water.