Acro tips burning all of a sudden, less polyp extension

[carpetlover]

So suddenly some of my acro tips are starting to burn and die, and some corals have less PE. All LPS and softies and monti unaffected.
Paras:
salinity 1.025
Temp 26.6°c
Alk 6.6
Nitrate 0
Phosphate 0.02
Mg 1220
Ca 460
All using salifert stuff.
Only recent change was increasing blues on the lights slightly and decreasing greens, reds and yellow.
What’s going on?

 

[Jekyl]

Zero nitrate is a place to start

 

[Uncle99]

Alk at 6.6?
That would be a problem
That’s lower than NSW.
Mine is 11

 

[carpetlover]

Alk at 6.6?
That would be a problem
That’s lower than NSW.
Mine is 11

Ultra Low nutrients. Normal alk for me and they were growing fast

 

[Kai K]

Your corals don't have enough food (nutrients and alk) to keep up with the increased light, so they get burned.
Turn the lights down a bit. Then take your time and over the course of a few days carefully raise your nutrients and bring alk to about 8.
When the corals show signs of health again, slowly ramp up your light to where you want it.

 

[Uncle99]

Ultra Low nutrients. Normal alk for me and they were growing fast

Yes, I fell for that UL stuff years ago. Corals starved slowly.
Now I run elevated parameters and elevated nutrients
Man, what a difference....never going back.