99.94% of all algae on Planet Earth occurs in our tanks due to either insufficient nutrient dosing or due to starvation of some element. Therefore, fundamentally, reducing the dosing as a result of the appearance of algae is false economy because inevitably this will make matters worse, not better.
The appearance of Staghorn is normally associated with poor CO2, however you advised that your dropchecker was yellow which, assuming you are using 4dkh water is an indication of adequate-high CO2. If this is the case we then have to look at flow or distribution. It could be that your filter throughput is insufficient, or that the effluent is placed in a disadvantageous position. What type of filter output do you have and how is it arranged? Another thing to look at is at what time does your CO2 come on relative to the light. Is the gas On 24 hours per day or do you use a timer. If you use a timer you need to turn the gas on an hour or two before lights on. What is the filter throughput rating of the filter? Also, how often do you do water changes and how much water do you replace? Do you normally clean the filter every so often? Do you vacuum the mulm from the substrate? All these issues can be factors.
Cheers,