Would agree with myka that you have too many fish for a tank that is 5mts old, it should be a written law that you only add a fish or two untill your tank hits the 1yr mark . Too many people want a fully functioning system in their first few months. It's a common thing to have algae ridden sand when your around the 3-6mth mark there's alot of things you can do as well but first some questions about your tank
whY is your lighting?? How long are your lights on and what light schedule do you use??
Post your tank water parameters
How deep is your sandbed???
Can you provide a pic of the algae??
What do you feed your tank???
Where are your powerheads pointed???
Did you use all liverock or a mix of live and dry???
Are to using tapwater???
If it's diatoms(brown) it would go away in time if you practises good tank maintanance ie..... Regular water changes, consistent light patterns , ro water
if it's cyano it could mean too heavy a bio load( too many fish) or inadequate flow etc, something dead etc. This can be removed manually or with reduced lphoto period and water changes, or by blackout
long hair algae tends to take anlittle longer to establish in your tank unless introduced from rock or from another tank. There's alotnof critters who much hair algae but it ges out of control fast so pull as much as you can if it starts to grow
if it's Dino then it's alot harder to get rid of but a pic would help to identify as it's quite similar to brown algae but like myka said it would be stringy with little bubbles
there are more types hut these being the most common in new tanks. All these algaes have one thing in common they will all feed off of excess nutrients so over feeding using tapwater not cleaning filters leavng lights on too long will all feed these algaes so if you do any of these then your first step is to reduce your nutrients. I've read mykas algae thread and I thnk it's a god place for you to strt reading then google these types of algae Nd read as much as you can on them
hope this helps I've left alot out but I'm typing from my phone so pls excuse anything I left out or my bad spelling lol
cheers