SPS Burnt TIP

[pelagic7]

It has been a while.. a few of my SPS got burnt TIP, and most of them are ok.. here's my tank info in past couple weeks

PO4 Hanna 736 0ppb
ALK Hanna 755 7.5-8.2
CA 420
MG 1400
PH 8.1-8.45
Temp:79F-80F
Salinity: 1.024-1.025

1. Tank size 6x2x2(180) + 150g sump , live rock 150lb-200lb sand 100lb
2. Filter sock. change every 2-3 days
3. SWC Mini Cone http://www.saltwaterconnection.com/i...c3fb33a1fe5119
4. WM Ecobak
5. seachem purigen
6. Carbon - change every 2-3 weeks
7. Algae Scrabber (just a small one.. for fun)
9. Light Cree XT-E RB x88, Warm White XM-L x 22, Bluex12 and Greenx12
White 11.5 hrs, first 1 hr 0%-100% last 1.5 hr 100%-0%
Royal Blue 12 hrs, first 1 hr 0%-100% last 1 hr 100%-0%


overflow area has some hair algae..
some SPS got burnt tip then covered with the Cyano. Most of the SPS are fine. I had some burnt tip issue before due to the ALK issue, but it's under control for a while now..

Can anyone help?

Thanks.

 

[Ptyochromis]

Take a chemical test of your alk and PO4 for accurate readings. How are your nitrates?

 

[pelagic7]

I haven't tested my nitrate for a long time, it's always 0.
I used hanna checker for ALK and PO4, and the readings are consistent for 2 weeks now.

 

[lighthouze08]

usually burned tip is associated with high alk, i would re-test your alk again. just my opinion

 

[swanny]

usually burned tip is associated with high alk, i would re-test your alk again. just my opinion

Low alk. as well. My alk. accidentally crashed to 4.75 recently and the tips of several started to turn white giving me the heads up to do a quick alk check.