The #1 algae trigger is decomposing organic matter. Remove all decaying leaves. Stem plants require replanting after pruning a few times. Unlike terrestrial hardwoods, older aquatic stems generally deteriorate over time. Remove and discard old stems and roots.
Instead of simply draining water, use a pipette or turkey baster to gently stir up detritus on the surface of plants and substrate. Take care not to stir up deeper levels of the substrate. Vacuum the detritus away while draining away around 40% of the tank's water.
Add a comprehensive 360 water conditioner directly into the tank and refill, taking care not to stir up the deeper levels of substrate. If you are keeping sensitive livestock, pre-mix the water conditioner in a separate container before adding the conditioned water into the aquarium.