brown "hair algae" and coral bleaching

Hey All,

I have been having a few problems lately and I think they may be related. For the past couple weeks, I have had a brown "hair algae" outbreak with strings on most rocks, corals, and the side glass. I am guessing this is diatoms. I thought they would clear up on their own by now but they are still here so I am getting worried. The tank is ~4 months old.
A second problem is the health of my corals. Over the past couple weeks they seem to be fading and bleaching (especially the birds nest and goniastrea). The birds nest is fading at the trunk and tips. I moved him lower in the tank but the white color has remained.
The fish, on the other hand, all seem fine. I have a flame angel, a percula clown, a purple dartfish, a yellowheaded sleeper goby, and a china wrasse.

Any thoughts?
Here are my params:
Temp - 77-78
salinity - 1.023
pH - 8.1-8.2
NH4 - <0.25
NO3-0
NO2-0
PO4-0
KH-8.8 (was really low (6.5) 3 weeks back and have been adding bionic alkalinity to get it up)
Mg - 1180 (in the process of raising)
Ca - 440

My tank is 120g with ~20g in the sump/fuge.
My lights are AI LEDs and they are on full strength for 8hrs a day.

Thanks for the help!

 

The tank is fairly young and seem somewhat unstable still, even though the volumn of water is good. I would shot for small changes over a week or so to bring the parameters where they should be for sps, other words one problems at a time. Start with the SG, next ALK stablilization and increasing your mg to facilitate that. Test for phosphates in your water source and TDS. If you could include a picture that would be great.

 

White tips and base sounds like an alk issue as stated above... But the faded colors are due to the tank not being that mature yet. To help this you can reduce lighting by an hour or two until you get a bit more mature.

 

Could the Alk issue also explain my missing nassarius snails? I started with ~30 and I now only see a handful.

Do you have any advise on keeping parameters stable?
I skim about half a couple of water each day (ATB 840 cone skimmer) and I have a topoff system that activates every 6 hrs. My salinty seems to drop by 0.001 every 2 days. I find myself continually adding 1/2 salt to the sump every two days.

My magnesium is rising at a very slow rate. I am using this aquavitro (same brand as my salt mix) Mg supplement every few days but I am still a long way off from 1350. The Alk rose right away from 6.5 to 8-9 after just a couple days of adding BIonic Alk.

The pH fluctuates between 8.1(night) and 8.2(day). I have never had it as high as 8.3 like many people talk about. Will this rise as Mg rises?

Ca, NO3,NO2,NH4,PO4 all seem stable.

Thanks for all your help!!