Algae can grow in storage tanks of water but usually when the water is not used regularly. We have had a 1000 litre IBC outside in sunlight now for 7 years. Periodically we check it for growth, there never is any. However the contents of this tank is changed very regularly, with it being almost completely emptied every couple of days. The water that goes into the tank is RO water, but not DI polished. Others findings may vary, but we have never had a problem with it.