Algae blooms can come from different imbalances in the tank. From not enough CO2 and O2 exchange, to lighting being too powerful or burning in the wrong spectrum, indirect lighting from outside windows, indoor lighting or other sources can contribute as well. Also, high nutrient levels in water, not allowing for proper bio exchange to occur can cause blooms creating green water or allowing hair algae to take over the tank. The best method to prevent algae blooms is a combination of proper feeding, appropriate lighting schedule and routine water changes.