Burnt tips on acropora?

[Dfost]

I have had this tank running for an over year now just recently had some issues with a few of my Acropora. Seems if some had some burnt tips recently and some having some minor flesh die off. I tested and the only thing out of range was phosphate which was .23 ppm. I have lowered it over the last month to about .12. some of the acros did not get bunt tips. I have not changed much recently other than adding a couple more lights to the display but I have ramped those pretty slow over the last couple months and the majority of the acros are getting anywhere from 250-350 par. I have recently added a refugium and noticed a difference in the tank overall. Now my main question is does elevated levels of po4 burn the tips of my acros or was it the lights? I move thing pretty slow in this tank focusing on stability and my Dkh does not move more than .05-.1 during a 24hr period.
Dkh 8.4
Ca 430
Mg 1400
NO3 6
Po4 .12
Ph 8.1-8.45
For flow in the display I’m getting around 51x turnover so I don’t think flow is a factor.

 

[Dburr1014]

Lou Ekos seminar clip.

Could be from the lowering of po4.

 

[Dfost]

Lou Ekos seminar clip.

Could be from the lowering of po4.

The burnt tips came before lowering po4. After I lowered the po4 I have noticed improvement. I generally try to keep the po4 below .08. I got busy and didn’t have time to check po4 and that’s when it climbed up. Trident tests everything else so I knew everything else was in check but started noticing issues when alkalinity was rising from slower growth due to the po4 I can only assume. Thanks for that clip is there a YouTube video on that seminar?

 

[Dburr1014]

The burnt tips came before lowering po4. After I lowered the po4 I have noticed improvement. I generally try to keep the po4 below .08. I got busy and didn’t have time to check po4 and that’s when it climbed up. Trident tests everything else so I knew everything else was in check but started noticing issues when alkalinity was rising from slower growth due to the po4 I can only assume. Thanks for that clip is there a YouTube video on that seminar?

Yes, you can search on youtube for a seminar or similar.

If you can keep everything stable, the tips can heal. It may/will help to tone down the lights a bit. I usually go about 10% lower for a week or two. Ramp back up after as long as it's not progressing.