Fern algae? Duncan dying, coral receeding

[craiguk]

Still battling clumping algae on the sand, and what looks like a fern algae on the rocks. Both my duncans are struggling (they are hardy, what would annoy them?). Getting flesh recess on some favia, acan, trumpet - but not all (see picks). Everything else: torches, frogspawn, zoas, plating monti and my one sps (birdsnest) all thriving. All corals have been in at least 1 year, often closer to 2.
Params: salt 35.3, temp 25.5, nitrate 0, nitrite 0, phos 0.07, kh 9.0, mag 1440, calc 400.
These are pretty much what my tank has been at for >1 year except 1) nitrate usually 10-20.. I'm assuming algae is making it 0. Phos is usually 0.04.
Any advice - either for algae (is it bryopsis? - do i need to add nitrate or will that make it worse?) ... and for corals.. I'm a little stumped. My leather had a growth spurt, I don't run carbon - could toxins really be the culprit?

 

[Timfish]

I'd start doing manual removal with water changes. The algae on the sand can be soaked in H2O2 for a few hours to a day, rinsed well, let sit for a day or two, then returned to the tank. Steel straws can be used to scrap and remove algae off rocks.

Don't add any kind of labile DOC, aka carbon dosing. There's a mountain of research showing labile DOC can have acute to chronic effects on corals and lead to their demise. Here's some links if you're interested:

"Coral Reefs in the Microbial Seas" This video compliments Rohwer's book of the same title (Paper back is ~$20, Kindle is ~$10), both deal with the conflicting roles of the different types of DOC in reef ecosystems. While there is overlap bewteen his book and the video both have information not covered by the other and together give a broader view of the complex relationships found in reef ecosystems

Changing Seas - Mysterious Microbes

Microbial view of Coral Decline

Nitrogen cycling in hte coral holobiont

BActeria and Sponges

Maintenance of Coral Reef Health (refferences at the end)

Optical Feedback Loop in Colorful Coral Bleaching

DNA Sequencing and the Reef Tank Microbiome

Richard Ross What's up with phosphate"

 

[Orito]

looks like briosis, I would look into fluconazole