I hate to be a pain, but it won't work.
Like I said, larger breeds need tanks bigger than a 25 gallon to be successful.
Smaller breeds (dwarfs) need like a 10 gallon with no corals and no live rock.
That limits you... to nothing.
If you wish to keep a tank for horses, set up a speices only tank. And research before so you can build your system around the horses.
Good luck, and like I said, I am not trying to be a pain.