The EI method doesn't use testing to determine how much of any nutrient to dose. When you decided to cut back to half the EI recommended amounts you stopped using the EI method. With 4 watts per gallon on any tank bigger than 10-15 gallons is very high light intensity, which will make the plants grow as fast as they can, limited by whichever nutrient they run out of first. I suggest raising that light higher above the water to reduce the intensity, or using fewer of the light bulbs. Then go back to dosing per EI.