Need help ID brown spots

[Edmund Y.]

Good evening!
I need help identifying the brown spots on the substrate as well as the dark brown coloring and red spots on the rocks.
Tank is about a year old
This started about 3 months ago when I increased light intensity to 65 percent and light color at 25%. About a week later this happened. Both overflow walls had brown stuff all the way to the top and the rocks had dark brown patches.
Did the 3 day blackout but did not really change much. Without lights the sand bed looks greenish. No bubbles or hair.
Light intensity back to my usual 25 percent max and color 15 percent max
Kessil 360
Photoperiod 8 hours
125 gallon
Parameters
Ammonia , nitrate and nitrite 0
Phosphate 0.01
Mg 1230
Ca 400
Alk 8.4
Salinity 1.023
Temp 78
pH 8.0
Feeding just once a day with reef frenzy

6 fishes
blue green chromis, pajama cardinal,banggai cardinal, blue hippo tang, maroon colored clown with yellow stripes, magnificent foxface

1 BTA
LPS corals, zoas, mushrooms, one leather, one coral I can’t identify

BRS GFO and B carbon
Took out UV a month ago

Thanks you and sorry if post is too long

 

[jordan be]

It looks like detritus. I think I spelt that right, lol. Siphon your sand bed and rocks next water change and it should help.

 

[Edmund Y.]

It looks like detritus. I think I spelt that right, lol. Siphon your sand bed and rocks next water change and it should help.

I tried it during my water changes and even took out some of the sand. They’re green colored. Did wash them and let it dry up and still green colored. The sand under that is white

 

[jordan be]

What's your clean up crew? It could be from extra nutrients in the water from over feeding

 

[Edmund Y.]

What's your clean up crew? It could be from extra nutrients in the water from over feeding

I have trochus, hermits, nerites, nassarius.
I only feed once a day with Reef frenzy
Equivalent to about half a cube.

 

[PDR]

I'm having a hard time seeing anything wrong. Could you take some pictures with the color at a higher percentage?

 

[Edmund Y.]

I'm having a hard time seeing anything wrong. Could you take some pictures with the color at a higher percentage?

The pic taken was on 100 percent for both color and intensity
Just used my phone.

 

[Edmund Y.]

The color of the rocks when I got them were kind of pink on the darker side. On the second picture they’re are red dots interspersed with dark brown patches. They came up after the light intensity was increased to 65. On the wall of the overflow behind was all brown. It has faded down slowly over the last few months
The sand is dark interspersed with white patches