Thats War!! but have you read this before?
How to beat Bryopsis
Here are some of the steps that you can take to beat this nuisance algae:
This is like a flow chart, so follow it and results will be found (eventually). Between each step, give yourselves 2-3 days of observation, then move to the next step. When making changes to your water chemistry, smaller bodies of water should be tinkered with over a longer period of a time than larger bodied water tanks (important). So if you have a smaller tank (under 70 gallons), any adjustments should be twice as long.
1. Elevate your Magnesium from 1600ppm to 1800ppm or 2000ppm. Do this very very slowly (over a period of a week) as it can have a very negative effect on your tank's inhabitants.
If that didn't work, move to the next step.
2. Elevate your Hardness (dkH) from 9dkH to 14dkH. Again, do this slowly over a period of 2-3 days.
If that didn't work, move to the next step.
3. Install (Purchase) a Phosphate Reactor. Two Little Fishes reactor is a perfect size. Use Rowa Phos media (or similarly potent media), under high flow through the reactor chamber.
If that didn't work, move to the next step.
4. Adjust your skim mate type. Change the way your skimmer functions, by adjusting how the skim mate comes out. You want it to be wet, for example, a translucent color. This will mean that you are over skimming, which is the idea as you want to get rid of nutrients in your tank.
If that didn't work, move to the next step.
5. Either purchase (or DIY) a Kalkawasser reactor. Kalk, or pickling lime, will bond to phosphates and will be skimmed out of the solution (with wet skimming). When setting up your kalk reactor, mix kalk and vinegar (100% all purpose) in a 2:1 solution. This is to offset the high pH of kalk. Drip it at a rate of 1 drop per 3 seconds. At this stage of bryposis removal, the kalk that is being dripped will lower Magnesium. So if the bryopsis is fully removed by this step, you will have to adjust your Magnesium at a later time.
If that didn't work, move to the next step.
6. Purchase a couple of Long Spine Urchins (Diadema Savignyi). Let them graze over this weak bryoposis. Some also found that Mexican Turbo snails will feed on this type of algae.
If that didn't work, move to the next step.
7. If you are not already using 20K lights, this is the time to switch. These lights will prevent algae in general from growing. Algae fester in spectrum of 10k and lower.
If that didn't work, move to the next step.
8. Some people say that rabbit fish (Siganus) will eat this stuff. At this point, you should have this algae in a very weak stage. The chances of a rabbit fish eating it are high. Some recommendations are Vulpinus, Magnificus, and Puctatus.
If that didn't work, move to the next step and at this point the last possible measure.
9. Take out the rock(s) that has the bryopsis, and soak it in RO/DI water. Do this for a period of 2-3 weeks. Change the water every 3-4 days, as the water will remove all phosphates from the rock. Make sure you have a power head to move the water in the container with the rock(s).
I hope it will help you some