ok i absoutly agree with b ball, just wanted to add a little more
if the tank is finished cycleing you dont NEED to have a protein skimmer but it helps, some say its a must have i think its a great thing but not a MUST, it would help cut down on nitrates that algae feeds off of
the cheapest way to cut down on algae, pending on what fish tank you have(fish only, reef)you can turn off the lights maybe a hour or 2 less per day, wont help much but it will a little
and last but not least uv sterlizers not only help with controling parasties but depending on how fast/slow the water flow is, it helps control algae as well