Brown row

[Alcasrac]

hi all, copoul of days ago i saw my sand is gettin brown, and rock as well. I changed the light intensity from 90% to 70%, 10am to 8pm plus 1hour blue (fluval marine light)
I have 14 crabs and now just only 2 pcs snalis, few snails is died after the crab attack... anyway. Yes so, the tank is 100gallons and plus 50g sump. This brown stuff coming quickly then the cleaner crew can clean.
My question is, what shall i do? The brown some place turn to green. This tank runing 4-5 weeks ago.
The parameters:
Salanity 1.025
Ph 8.2
Kh 8
Nitrite 0.2
Nitrate 5
Ammonia 0
Ph4 0.2

Other thing, the nitrite is never go to zero after 10% of water change is 0.1, i never saw on zero. This is gonna be trouble?
Many thanks for help

 

[ndrwater]

You've got some diatoms growing. Perfectly normal. Just tells you things are progressing as they should with your cycle.
I would suggest lowering your lighting intensity a bit more. LED's, including the Fluval are quite powerful. Getting corals to acclimate to higher intensity settings takes quite a while. Starting lower and ramping up as necessary is a better path to success.
Welcome to R2R!! keep the updates coming!!!

 

[Alcasrac]

Cool cool, the brown is gettin slow down, i did the light only 50% intensity, and some place getting green . The sand on some place 1-1,5 cm deep brown. And couple of sand is purple, i mean looks purple.

My other question is
I would like to take sand shifter starfish, but i can’t find good info about, when can i add. What is minimum running life for the tank?