Algae is a plant that will grow anytime you have water & light in the same spot. Because algae is a plant, Algae killers will kill your plant first. There are a couple new products out that help stop algae from growing in the first place, but the cheapest & easiest way to stop algae is to block the light. If algae is growing on the top of your container you would take a piece of plastic on the top of the container blocking the light from getting through. A healthy plant will block the light on its own with the plant canopy. Cleaning the tray at least once every couple of week will prevent algae from having time to grow.