I have and am currently using the Tech M treatment for my 180G reef tank to tackle bryopsis. I tried the cutting back feeding, cutting back lighting, running the skimmer wetter, adding phosphate removers, adding a sea slug, adding a fox face, etc. NOTHING would get rid of it, so after much skepticism, I finally broke down and went the Tech M route. Glad I did. I introduced a really nice piece of live rock to my tank that had some great macros, but hidden under it was a lovely clump of bryopsis that I didn't notice, and it started sprouting in my tank. My MP40's made sure that it spread EVERYWHERE!
IF you have a fully stocked tank, raise the Mag levels SLOWLY and then keep them at 1600+ppm (I'm keeping mine at about 1650ppm steadily) and keep them there for two weeks. If you raise your levels slowly over a period of a week or so (depends on how low your starting number is, mine was around 1250ppm), then you're less likely to have invert loss. If you raise it quickly, the algae will die off faster, but you'll have much greater invert loss. I have only lost one Florida Fighting Conch from this procedure. My shrimps (harlequins, fire and skunk), all snails (nerites, nassarius, bumble bees, periwinkles, trochus, florida fighting conch [lost one of 3]) are fine, my clams are fine, my brittle and chocolate chip star are fine, my corals are fine, my other macro algaes that I want to keep are all fine, only the bryopsis has been effected. If you're at the end of your rope with the bryopsis battle and have exhausted all other options like I did, the Tech M treatment really does work. I'm not a fan of chemical dosing, but sometimes, you just need to do it. In a barren tank, I'd go with the shock of just raising it quickly and holding it there. As it starts to die, remove what you can manually, don't let it just float away.
Do yourself a favor: get all the needed Tech M up front, the gallon size bottles can be hard to find, and I've easily went through 2 gallons already and I'm not done treating. My total tank volume is over 200G, but still, you're going to need a lot, so make sure you have all you need from day one. You don't want to get half way through the treatment, finally getting a handle on the evil bryopsis only to have to stop treatment and it all heals and grows back.
Forgot to mention, I also have a TON of mysid shrimp in my refugium that don't seem to have been effected by the Tech M treatment either.
