1) High Mg initially to weaken the bryopsis. Like many said before, this alone is not enough to keep your tank free of bryopsis on the long run . As soon as Mg starts to go down bryopsis is likely to return unless further measures are taken
2) Intense and varied herbivore pressure: mexican turbo snails, astrea snails, trochus snails tiger cowrie, diadema urchin, hundreds of hermit crabs, sally lightfoot crabs, emerald crabs, desjardini tang, kole tang, foxface, and rabbitfish
3) UV sterilization: theoretical effect on bryopsis spores. I'm not sure that this had any effect in my tank
4) manual removal to decrease the bryopsis load. You must do this with all the flow in the tank halted and make sure that no fragments get away, otherwise you will aid in its spread
5) High pH and high alkalinity. I switched from a calcium reactor to a kalkwasser reactor. The average ph in my tank went from 7.8 to 8.4. Since then, I have noticed a very marked increase in coral and coraline algae growth and a decrease in all forms of micro and macro algae.
6) Keep your bulbs new and switch out before the spectrum shifts to yellow. I believe that In my case old bulbs coupled with excess nutrients are the reasons that I got the bryopsis outbreak in the first place ( although that is difficult to prove, the outbreak seemed to coincide with the above)
6) effective nutrient export: strong efficient skimming, high flow : in my case this made a huge difference. I upgraded my skimmer to an ATI bubble master and my bryopsis never came back
Obviously there will be others that will disagree, but this protocol worked for me and my tank has been bryopsis free for 4 months now ( I hope I did not just jinx myself)