My macro is under 2-10k T-5's. I have to trim probably once a month or sometimes sooner. I have Caulipra, Halimeda, Chaetomorpha, and Red Feather. The feather and the Halimeda doesn't grow that fast but the Chaeto and Caulipra does. Hopfully as soon as i can find some i will have sea lettuce too.
I had a 65w 10k
PC and the stuff didn't grow that fast. I changed it and it did so i would say check your light and it will probably grow fairly well but it needs to have a good amount of flow so not sure how that would work in a horse tank.