It looks to me like you are 50% too much KNO3, but ok on the others. I would ignore the sump volume and dose accordiing to the volume containing plants. So, 125 gallon tank gets 1.5 tsp, 3X per week. You have about double that amount of planted volume, so that would be 3 tsp, 3X per week. Then X 3 to get weekly total, and divided by 7 to get daily dose, or about 1 1/4 tsp per day.

I would also start dosing the full amounts from the beginning, and rely on the 50% weekly water change to take care of the excess.