[Update 4/27/17: This setup with the pump-filter unit sitting on a plastic mesh with water dripping back into the tank through the mesh didn’t work out. Salt creep on the mesh was a major problem. See the configuration I’m using now.]
So far so good. This pump+filter on top of tank seems to be the only setup that works. In variations that had the pump+filter on the table next to the tank, leakage was a constant problem. In this on-top configuration, I’ve had no leakage problems. Yet. The opae seem to love it. They’re very active all day and night. Breeding has been taking place in the 1.5 gallon, but I think it’s accelerating under this new setup. The trickle filtering seems just about right. The 10-gallon, which I’ll be covering soon, is also set up with a single pump+filter unit on top of the tank, and it seems to be doing fine. Again, the opae are very active day and night. The 18-gallon has two pump+filter units, and it, too, is doing fine. I’ll be covering this tank soon, too.