New Tank sand turning brown. Need some advice

[Philrock]

I recently purchased a Red Sea s650 max 8 days ago from someone getting out of the hobby. We broke it down and moved everything in 1 day. All the fish and coral and rock you see where put back to original. All fish and coral survived. Replaced the sand bed with live Fiji pink sand and had to add about 100 gallons of Nutri-Sea water live ocean water (purchased). Also saved his chaeto for sump. All levels tested good last week and again yesterday. Everything has been going well did not loose anything in move. Today I noticed the sand is turning brown. Mostly in shaded area. I do have the 3 redsea led90 lights running about 10 hours with 4 hour moon.
Sump looks good. Protein skimmer looks good. I did read that new sand will do this. Question. What should I be worried about and what should I do to be proactive. Thanks in advance just got back in the hobby, been out for 20 years so a lot has changed. Any help would greatly be appreciated.

 

[F4u-SuperCorsair]

Take a pic with a white light so people can see the sand bed better.

 

[twentyleagues]

Well looks like you got yourself quite the tank there! Agree white light pics needed for id. By the sounds of it probably diatoms they will pass. What do you have for cuc?

 

[Philrock]

Well looks like you got yourself quite the tank there! Agree white light pics needed for id. By the sounds of it probably diatoms they will pass. What do you have for cuc?

For CUC I have about 15 Nassau snails. A gobi 2-3 hermit crabs. I do have some larger snails that do everything. And 2 fire shrimp. Also Naso tang, blue hippo, gem tang, black tang. All are about 6”. Along with fox face and a copperband.

I am guessing I just need to let it run it’s coarse.

 

[twentyleagues]

Probably diatoms but without a micro scope you wont know for sure. Being that fast at showing up and the fact you used new sand is why I say diatoms. It could be dynos too hard to tell from pics but if it starts to get stringy or has bubbles in it thats a good sign of dynos.