Can’t grow Cheato... best alternatives?

[Reef AquaCult]

I also have both chaeto and ulva and the ulva grows more than twice as fast as the chaeto, so you may Be experiencing the same thing. As you mentioned the ulva acts as good food for herbivores so this might not be a bad thing. I would say you may just be recycling your nutrients in your ulva / tang cycle which is a positive in my view. If your ulva is growing than its doing the same thing the chaeto would be doing, and it’s also a good food source! I wouldn’t change much as long as you have a good strong grow light.