This is good, but as mentioned you will still need phosphates (mono potassium phosphate, or using the IUPAC name, potassium dihydrogen phosphate).I bought and am using the "Macro Micro Nutrient Mix" from:
Magnesium sulfate (Epsom salts) will raise the hardness of your water.It looks like it already has Magnesium Sulphate.
What does magnesium sulphate do exactly?
I think my tap water i use is hard. How do i make it soft without harming fish and plants? You mentioned epsom salts. Do they make the water harder or softer?
If you already have hard water, it would be best to omit the magnesium sulfate, but this is difficult since you are using a mix (this is why buying each chemical individually is usually better than buying a premix).
In order to make you water soft, you will need to use RO/DI water (and perhaps mix with your tap water).