Algae are easily produced by light and nutrition, the best way to prevent them is cover the holes of the planting plate that light could get into or anywhere with nutrition.

If you already saw lots of rotten plants roots or algae on your hydroponic system, it's time to clean your machine, you need to remove the rotted or infected plant immediately then replant after cleaning/drying the unit, spray with alcohol and wait for 3-5 days, then start a new planting cycle.

If algae is on the sponge, maybe it’s because the sponge being too wet. Adjust the water level so that it does not reach the top of sponge, try to dry the surface of the sponge, that can decrease the algae.