Hi,
1 Litre = 1,29 KG, so the density is 1,29 g/ml.
6% DTPA-Fe. So 1 ml of that fertilizer contains 1290 mg * 0,06 = 77,4 mg DTPA-Fe.
A solution of 250 ml with 0,05 mg/L Fe would be really lean. Maybe do you mean to add 0,05 ppm Fe directly to a 250 Liters tank? In this case
250 L * 0,05...