how long has the tank been set up? If it just recently, you probably had an ammonia bloom. Just keep the ammonia lower than 0.25ppm at all times and your residents will be fine.
also, how long does your light turned on? if it is an algae breakout, you could probably lower the photoperiod to 8 hours. More than that might be the reason for the algae, if indeed it is an algae breakout.