Algae issue - New tank

I am in process setting up 55 gallon hex with Lionfish and corals only. Tank is in process of cycling and in past one week huge algae formed on sand bed.

Tank has :

60 pounds coarse aragonite sand, 30 lbs of live rock and 30 lbs of dry marco rocks.

Aquaclear 110 HOF with carbon and seachem de-nitrate.(planning to convert this as fuge later)

Aqua remora C skimmer

120W chinese RGB LED

koralia evolution 1050 powerhead

no sump or fuge as I don't have option to keep any. Tank has been setup for just over 3 weeks and no creatures in it. Attached pics and video, what could be issue. Looks to me not diatoms or cynao, is that green hair algae? but they exists only on sand bed and I have very good flow, you can see algae constantly moving. RO/DI water being used, tested 0 in my tds and tested nitrate only around 5ppm. please help me , it looks very nasty.

Video link https://picasaweb.google.com/107625970015049289592/Algae_hex?authkey=Gv1sRgCNbj086R8uS_Ew

 

forgot to mention, it was lusty green and after cutoff light for 48 hours, now they all turned brown but not dead yet still waving nicely

 

Seeing as how you have no method of nitrate/phosphate reduction like a fuge/GFO/biopellets, the only way to reduce nutrients for you is through regular, large waterchanges.

Algea popping up during a cycle is completely normal. When your cycle is done, manually remove as much as possible and do a large waterchange.

 

i am not worrying much about setting up fuge since my bio -load going to be very less, just one dwarf lionfish and corals. once tank matured, if nitrates exists my plan to use vodka dosing, i had bad experience with bio-pellets in other tank. but is this regular new tank algae issue? does not look like diatoms which is common new tank setup issue.

 

My tank just finished cycling, and I have a bright green slimy algae covering some of my rockwork. No diatoms yet (those will come in a few weeks). Everyone sees something different, but if there's one thing for sure, you're going to see algae. lol

Depending on what you want for corals, you might want another powerhead. You're only getting about 20x turnover right now...

 

If its algae as part of cycling I don't care..regarding flow it may be little less for regular tank but for hex I see it's too much..