yea I would put 3 horses in a 10 gallon, and they are very difficult to keep, and I doubt they like the fake plants usually they live in sea grass, they need very low water flow so they dont wear themselves out battling the current, they are very specific eaters, and need a species only tank which you have done but I would make it a little bigger tank, and make sure there are plenty of "hitching posts" for them to attach themselves to