Sps troubles

[jmp21677]

So I've been struggling with sps for a while. They have always been my Achilles heel. I'm hoping someone cam give some ideas of where to go next?
Tank - 50 gallon waterbox cube
Power heads - 3 mpw10qd
Lighting- Radion G4 Pro with 4 T5 supplement (par 400 at top, 140-200 on bottom)
Nyos Skimmer

LPS seem to do well as do zoas. I did recently have a elegance polyp bail but only recent loss.
Sps are a disaster. They just seem to fade away. Type, level in tank etc, nothing seems to help.

Tank parameters
Alk - 8.4
Calc - 425
Po4 - .05
Salt- redsea blue bucket

 

[Camaro Show Corals]

How old is the tank?

 

[jmp21677]

Tank is about 18 months old. The system has been together about 3 years. This was an upgrade from a red sea 170. I recently bought a burning banana frag. It looked good for about 2 weeks then polyps stopped extending and the tissue faded. Soon after tissue recedes and its gone. Seeing the same issue with chalices right now as well

 

[NS Mike D]

NO3?

lets rule out that they aren't struggling to get the basic building blocks

 

[jmp21677]

I'll test NO3 tonight and see what I get. Started testing last night and realized it was expired by two years

 

[jmp21677]

Test NO3 and its at .05