You want a bottomless tank right? As in no substrate? Then I’d consider any of the Fairy / Flasher Wrasses over a Halichoeres or a Leopard Wrasse as they need to sleep in sand. I’d also not do gobies as they also like sand. The Gobiodon sp. could be exceptions but I’ve heard they’re not the hardiest and easiest to feed unless you have a very healthy specimen from the get go and can get it to eat prepared foods.
The Powder Brown needs to be in at least a 6’ tank long term. Call it one of my pet peeves, and no offense intended, but I’m not a fan of seeing fish in tanks too small for their adult size unless the reefer has at least somewhat of a concrete plan to upgrade to a system suitable for that particular species’ adult size.
Assuming your 75-gallon is a 4-foot tank, you could fit in a Bristletooth Tang except for the Spotted (Blue Eye) Bristletooth or the Striated Bristletooth or the Chevron. This means a Tomini, Yellow Eye Kole, Squaretail, or White Tail would be the suitable Tangs for a 75. A Zebrasoma really needs at least a 6’ 125 long term IMO though I’d probably put a Black Longnose or Yellow (the smallest of the Zebrasoma Tangs) in a 5’ if given enough swimming space. Purple, Scopas, Gem, and both of the Sailfin Tangs need larger tanks.
You could look into a dwarf angel, a more active blenny like a Midas Blenny, a smaller shoaling fish like a couple of Pajama or Yellow Striped Cardinals, or if you’re willing to feed frequently and have a good QT routine, a smaller species of Anthias (not an expert on them). Chromis (Blue / Green, Black Axil, maybe some of the smaller lesser known species) are OK too if you can QT for uronema but there are mixed reports on how well they do together as a group.
Any of the smaller basslets can fit into a 75. Royal Gramma, Black Cap, Swissguard, Swales, Yellow / Randall’s / McNeill’s Assessors.
If you want to do something different, assuming a 4’ tank you could have a Marine Betta. They get to 8” but aren’t very active fish. Still for bioload purposes I’d keep a 75 to 2 larger fish (6” and above) at most and this is assuming a 4’ tank.
A group of Scissortail, Zebra, or Blue Gudgeon Dartfish will likely not kill each other in the way Firefish do.
Damsels. Yup. You could have (maybe) a pair of Chrysiptera sp. damsels, just avoid the Blue Damselfish (C. Cyanea) and Fiji Devil (C. Taupou) and stick to Yellowtails, Azures, Talbot’s, Rolland’s, maybe Starckis if you can find them but I don’t know much about them.
It all comes to whether you like more smaller fish or some larger fish but a fewer number of fish overall. Also, how much do you care about a clean up crew, shrimp, snails and so on?
A couple of of Fairy and Flasher Wrasses along with your Clownfish pair, a basslet, a smaller Tang or a Marine Betta, and a smaller shoaling fish like Cardinals or smaller Anthias or Dartfish, a Midas Blenny, and maybe a pair of more peaceful damsels would work nicely IMO. Bangaiis pair off. Pajamas and Yellow Striped I think tend to stick together more.
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