hope this helps and Welcome to ILGM
The first thing that you must take care is, block all sources of light penetrating the hydroponic medium. Make the nutrient reservoir, channels, and entry and exit points of the solution absolutely light proof. You can do this by covering them with an opaque material. You can purchase algaecide products from the market and use them as recommende or contact Emerald Harvest for extended support. A moderate amount of hydrogen peroxide is also capable of killing algae. However, make sure that young plants do not come in contact with hydrogen peroxide. Some of the natural methods that you can implement to control algae are: incorporating barley straw rafts in the reservoir and adding grapefruit seed extracts to the nutrient solutions.
It is always better to take every possible precaution to prevent growth of algae, instead investing on chemicals for eliminating them. If the growth is dense, then you have to clean the reservoir and refill it with fresh nutrient solution.