My tank is 270g and I run a 114 watt unit on it. I had a 57 watt previously without success. Once I upgraded to the 114 watt Ostreopsis, Coolia and Prorocentrum were cleared out pretty quickly. I personally use an AquaUV brand. Pentair Aquatics is another decent brand as well but I have no personal experience with them. Be prepared though, they aren't cheap.
Thanks. I realized after I sent my last reply that it was your post I saw that in. I don't have the cash right now for that kind of sterilizer unfortunately. I guess for now I'm stuck with elevating Nitrate and Phosphate and increasing my biodiversity.