The brown algae u r refering to is diatoms. They r normal for a tank that has or is almost cycled. Usually they will fade away after the cycle and water changes. Don't do water changes f u r still cycling, u will just prolong the cycle.
LS has beneficial bacteria and living creatures in it. When u siphon it out, u r losing sand and taking out benificial bacteria. Just buy a clean up crew and they will clean it.
