Excess lighting, nutrients, and poor tank conditions promote algae. To reduce the risk of an algae outbreak in aquariums it requires the following.
Lighting - By monitoring the amount of light your aquarium is exposed to helps against algae, by simply cutting down the time the lights are on is simple to do with a timer. If you have your aquariums light on for long periods of time can contribute to algae, so say the light is on for 12 hours a day, then try cutting it down to 8 hours a day.
Nutrients - By starting a dosing regime, and sticking to it helps in the fight against algae. Starting with the amount of nutrients in your tank, if you "dial" in on your dosing regime means that you're putting in enough nutrients so that the plants quickly soak up the nutrients before algae can use them.
Tank Conditions - By following a weekly schedule of a fertilizer regime combined with weekly water changes helps fight against algae. Water changes are normally 25%-30% once per week helps to remove the excess build up of available nutrients, which is why you see them discussed in the dosing regimes.
15g Fluval Flex - Will be a planted shrimp tank