The poroblems with red algaes are that they are fairly slow growing. You want algaes that grow quickly. The faster they are growing, the faster they are absorbing nutrients from the water. That's why green algaes like caulerpa and chaetomorpha are more commonly used in refugiums, because they are fast growing. The problem with them in a main display tank is that fish like to eat them, especially tangs, angels and rabbitfish. Not much will eat chaetomorpha except a rabbitfish. Its a little tough to chew on. Caulerpa on the other hand has a tendency to go sexual in a display tank where the lights go on and off. They can produce some toxins when they go through this stage. That's not a problem in a fuge where the lights are on 24 hrs.