"Excessive" nutrients doesn't cause algae. Usually a shortage of nutrients slows the plant growth and that can lead to algae. I think you are way too low on nitrates, if you are dosing 3-4 ppm. Most of the problems we run into with plant growth are caused by not having enough CO2 in the water, and not getting the CO2 enriched water in contact with all of the plants, so I suggest watching the plants to make sure all of the leaves are moving a bit in the water current. If the drop checker has 4 dKH distilled or deionized water in it, and is yellow, you have plenty of CO2 in the water where the drop checker is.