UV sterilizers are a great tool for water quality management, killing free-floating algae, and promoting sound fish and invert health. I don't believe that they have any significant negative effects on reef tanks. UV and ozone are beneficial in the fight against algae, but don't expect a night & day difference.
A well established system will have ample zooplankton in the display tank, so the few stray copepods & mysids that migrate from the refugium, aren't a big part of the fish and invert diet. The amount of food that we import daily is far greater. In addition to this, zooplankton rise out of the substrate at night to provide supplemental live food for corals. The contact time and wattage of the UV is likely to be insufficient to kill them, and their larger size may offer some additional protection.
Bryopsis is a bugger. It comes in on the base of Bali aquacultured SPS, and some bali corals. I've considered hacking off the frag plug when they come in, to break the cycle.
I don't remember encountering it before 2000; perhaps it was introduced with new collection sites or mariculture facilities in tidal areas. Before that, derbasia was the scourge of reef tanks. I prefer derbasia because it's less toxic, and therefore palatable for many fish and inverts. I haven't seen derbasia since bryopsis came on the scene, and assumed the role of house cyanobacteria. Incidents of red cyanobacteria have also dropped off dramatically.
Sometimes bad things happen to good tanks. Bryopsis is fueled by poor water quality, phosphate and high DOC and POC, but like any bacterial infection, it can strike indescriminantly. Once it gets a strong foothold, it is able to sustain its' population, independent of bulk water nutrients. As some parts recede, others flourish. Bacterial algae needs to be treated like any other bacterial infection, and fought on all levels.
One cause for bryopsis blooms is carbon fixing due to residual carbonic acid from calcium reactors. Check your CA reactor effluent.
I've heard reports of staving it off by starving it of nutrients, but I've heard just as many claims of it crashing in time on its' own. I believe these two claims to be one in the same. Time was the ultimate cure in each case, with a little help wherever possible.
There are many reports of lettuce nudibranchs and sea hares being employed to create a level playing field, but this has not been my experience. Physical removal seems to be the best catalyst to a cure. It tends to grow in different forms according to aquarium conditions. If you re lucky, it will grow from one small thallus at the base, but it looks like you have a more stubborn form. Part of the problem is that bryopsis has a unique ability to quickly seal itself off when severed.
Erythromycin doesn't affect it, but there is likely to be a reef safe antibiotic out there that will. I've been meaning to do some experiments with neomycin and chloramphenical to see if they aid in the battle. Once you get the population down to a minute amount, good water quality and low phosphates should leave no room for it in the ecosystem.
If you don't have a lot of coral, you could try removing them to another tank, and turn your display tank lights off for a week.
Unfortunately none of this advice adds up to a quick cure.
