Apollo sharks, Luciosoma setigerum, are schooling predatory fish from Southeast Asia. They are excellent fish, but they are pretty big (around 15-20 cm in captivity) and need masses of swimming space. I kept a group in a 200 gallon tank, and even there they looked confined. They must surely be among the fastest freshwater fish in the world: they are beautifully streamlined and move with extraordinary grace. They are prodigious leapers, and have to be kept in a covered tank.
They do have lovely colours, most notably the copper spot on their nose that really catches the light. They're somewhat predatory, and while happy enough on pellets and regular flake, will certainly eat small fish given the chance. Wild fish are apparently fish-eaters. Otherwise completely peaceful, and they make excellent companions for midwater fish too large to be eaten, such as gouramis, dwarf snakeheads, barbs and the like. On the other hand, don't mix them with any surface dwellers that don't like activity. Hatchetfish and African butterflyfish would be tragically poor choices for tankmates.
Water chemistry largely irrelevant, but lots of water current is mandatory; I'd suggest filters and/or powerheads that produce not less than 6 times the volume of the tank in turnover per hour.
Cheers, Neale