Stronger lighting is always better, until you start "burning" the algae. Burned algae will be yellow, because it is getting too much light but not enough nutrients from the flow. More light requires more nutrients, which give you more filtering.
So if you have yellow growth, increase the flow so that more nutrient are delivered to the algae. If you can't increase flow, then add some iron. If you can't add iron, then reduce the number of hours the lights are on. Do not reduce the wattage, however; stronger light for less hours is better than weaker light for more hours, because weaker light will grow darker algae. Stronger light grows bright green algae, which does the most filtering.
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