For the liquid form, 50ml, giving 100ppm of Fe-DTPA.
Just dilute to the necessary for your required usage.
If you need 4ppm, just take 2ml of the solution and dilute with 1 litres of water.
You can also take 20ml of the solution and mixed with 10 litres of water, or the whole 50ml with 25 litres of water to yield 4ppm.
You need to do your sum, formulation and chemistry in order to know how much to use. Else, purchase the liquid form