Need help troubleshooting kh / po4

[heifinator]

Been having some issues recently with my SPS tank. Just wanting to see if the bright minds at NR have any ideas.

 

Some info.

 

65 gallon 40x24x15 high.

20 gallon sump

 

Light is approx. 450 par top third, 250 middle third, 125 par bottom third. Lights ramp up for 3 hours, run for 5, then ramp down for 3 hours.

 

Ammonia: undetectable

Nitrite: undetectable

Nitrate: undetectable

 

Calc: 380-420 ppm

Alk: 8.2 - 8.7 dkh

Mag: 1300 ppm

 

Temp: 79 - 80 f

Salinity : 1.025 sg

 

Feed mysis 4 times a week and dose a/b redsea nutrients daily 10ml each.

 

Run gfo 5tbsp and carbon 5tbsp in BRS dual reactor. I dose 2 part once daily during ramp down. About 10ml each.

 

Everything was great except I had a daily algae bloom on my sandbed every day for a few months. Started to bug me greatly. Stopped the amino acid dosing and increased GFO some.

 

I started to notice stn on tips and bases of SPS especially caps. I have about a .5dkh swing daily. I tested po4 during night when bloom is gone and it always reads 0.00ppm.

 

I was fairly sure the issue was nutrient related aso I did 2 20 gallon water changes 3 days apart. No improvement. The SPS scream of being nutrient deprived from what I've seen in the past. However algae contradicts that...

 

Thought about dkh swing but .5 didn't seem to be excessive.

 

Any ideas greatly appreciated. I'll provide any info needed, I'm sure I forgot something.

A

[seabass]

Do you have pictures of said algae? Is it brown and slimy? Dinos?

 

GFO can reduce alkalinity.

 

The goal isn't to depleat the system of phosphate. Low phosphate can actually cause problems with coral health. Plus if you do have Dinos, this can further cause health problems.