tiny brackish top feeders?

Most livebearers are either brackish or can adjust easily, but I suppose that's what you meant by "guppies etc". You can also look into certain killifish and rainbowfish - I've kept Diamond Killis once, they get to about 2" and will eat flakes.

I should also point out that Glassfish are either brackish (they can adjust of course) nor surface dwellers/feeders.
 
I wouldn't go with halfbeaks, they require more space than a 10g would offer, and are very sensitive to changes in water parameters.
 
Smaller brackish tanks are tough, I found that, aside from guppies, most brackish fish seem to get big to very big. I have the mollies in my tank and they are all over, but probably too big for a 10. The bumblebee gobies are cool but not top feeders.

I read an article where they were catching glassfish in native brackish waters in India. Don't know what the sg was though. I've heard that the indian mudskippers stay smaller than the atlantic mudskippers, but I would assume still not small enough to go into a 10gal.
 
Why not just stick with a school of glassfish?
 
Glassfish do okay in both fresh and brackish, though usually sold in freshwater, it'd need some level of acclimation. They're also picky eaters, and hang mid-to-bottom as opposed to the surface. Indian Mudskippers are way too big for a 10g, and would also need a beach-like setup.
 
even though I'll have a beach like set up, I am not considering mudskippers because I know they are too large for the tank. (the tank is a 15 g, with 10g of water..)

aclimation won't be a problem, as I am starting the tank freshwater and going to transition to brackish over a month. it will be very mildly brackish, just enough for the inverts to have what they need. BBgobies are really attractive to me, but with inverts I'll end up with a tank full of bottom dwellers hiding all the time. I may go with just glass fish, but haven't even seen them locally. I guess I could get 1 guppy, but I'm not interested in breeding them. if any breeding happens in this tank, it will be amanos.
 
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