Hi oohnoo,
With those dimensions, it is actually a little tricky. The Hydra 26 definitely has enough light and coverage for your tank. However, due to the single-puck design, it is going to have a noticeable amount of light spillage front to back as it is trying to cover a 24X24 area. If you don't mind the light spillage, the Hydra 26 would definitely work fine for your aquarium.
On the other hand, the Hydra 52 with the two light pucks, will allow you to bring the lights closer to the tank and reduce the amount of light spillage. Having two separate pucks will do a better job covering a rectangular area as you get less light spillage and less shadowing.
For the Hydra 26, you will want to mount the light 10"-12" above the aquarium. For the Hydra 52, 6" - 9" should do the trick.
If price is not a factor, the Hydra 52 would be the better option. However, the Hydra 26 can definitely do the job as well.