Hello friend.
I had the same issue in my RS-525. It lasted for months trying to do it the pick and add things way. I removed as much by hand as I could get and then used a tooth brush to brush the rocks. I then used a siphon from DT into sump but ran the water thru the filter sock so I wasn’t doing a massive water change but would keep filtering what was rubbed off.
Then I used attached picture and followed the direction. Turn off skimmer for 2 weeks during this process. Mix it in a bowl and then add to your DT. After 10 days I did a 3 day black out at the very end (turned off all lights) and only allowed natural light in. At the 14 day period it was all gone then I did another brush with tooth brush and a 20% water change. It literally got it all out (100%).
The first time I tried it a few months ago I didn’t do all the steps in the paragraph above. I only mixed and added and waited and it helped but didn’t remove all. The second attempt above with all the cleaning before and the black out worked 100% for me.
This DID NOT AFFECT MY FISH OR CORALS.
Hope this helps. You can search my name and see I posted about this a few times to others.
I had the same issue in my RS-525. It lasted for months trying to do it the pick and add things way. I removed as much by hand as I could get and then used a tooth brush to brush the rocks. I then used a siphon from DT into sump but ran the water thru the filter sock so I wasn’t doing a massive water change but would keep filtering what was rubbed off.
Then I used attached picture and followed the direction. Turn off skimmer for 2 weeks during this process. Mix it in a bowl and then add to your DT. After 10 days I did a 3 day black out at the very end (turned off all lights) and only allowed natural light in. At the 14 day period it was all gone then I did another brush with tooth brush and a 20% water change. It literally got it all out (100%).
The first time I tried it a few months ago I didn’t do all the steps in the paragraph above. I only mixed and added and waited and it helped but didn’t remove all. The second attempt above with all the cleaning before and the black out worked 100% for me.
This DID NOT AFFECT MY FISH OR CORALS.
Hope this helps. You can search my name and see I posted about this a few times to others.

You have to leave it in for at least 3 weeks and if phosphates get high I used phosphat-e from brightwell once and with nitrates I feed less as during treatment as no water changes . Plus adding microbactor 7 was a big help which i believe in your case would have probably out competed you cyano before it started . I added about every three days during and I stopped after treatment because it was helping to zero out my nitrates . If I ever end up with bryopsis again I will use flux rx without hesitation . But that’s my choice and others will be reluctant. I was at first but got tired of it coming back after manual removal . It also took out gha . During treatment i felt it was important to run my skimmer without the cup , keeping the water well oxygenated . I’m sure a airstone would have worked as well .

