Can you provide some details, then we can advise how to deal with the algae issues?
Flow (powerheads rating LPH)
- what you got?
- if T5s, what overall wattage, and how old are the bulbs?
- how long are they on for?
Feeding - what and how much do you feed, and how often?
Stock - what fish have you got?
Believe it or not, all of that will have an impact on algae growth. Algae needs light and a food source (normally nitrate and/or phosphate). Remove either of those, and it will die off. You can't remove light altogether (you can for a couple of days to give it a hit, but not long term). However, you may have the lights on too long, or have old bulbs, etc. and that can be fixed. Nitrates and phosphates can be reduced to starve it too.