Thanks everyone.
Today Ocean moved into Kelsey's old 'apartment'. Aqua is in a decent-sized bowl next to the tank (since it only has four areas for the Bettas, and I didn't want to tease Aqua by putting her in a small compartment in the tank while the others are swimming free), but of course only after a water change.
I still miss Kelsey, but I guess that's selfish of me, I mean, at least he's free of pain now. I bet he's swimming around in a nice bowl with endless boundaries, and tons of ornaments!

Thanks for the kind words everyone.