[Darkblade48]

I bought and am using the "Macro Micro Nutrient Mix" from:
http://aquariumfertilizer.com/index.asp?Option1=cats&Edit=2&EditU=1&Regit=2

This is good, but as mentioned you will still need phosphates (mono potassium phosphate, or using the IUPAC name, potassium dihydrogen phosphate).

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?

Magnesium sulfate (Epsom salts) will raise the hardness of your water.

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).

 

[Darkblade48]

What does it mean when they say "GH Booster"? Does it make the water harder or softer?

The GH booster is used to boost GH (increase GH, make your water harder); this may or may not be required depending on your water parameters.

The composition of the GH booster is: 2 (K2SO4) : 2 (CaSO4) : 1 (MgSO4)

 

[Darkblade48]

Thanks for the explanation. Sounds like i dont need it yet. Are there any ways to soften the water instead of harden/boost it? (aside from water changes from tap / RO/DI water).

No, that really is the only (practical) way.

I guess the alternative is to move to a location that has softer water.

 

[Darkblade48]

So my KH2PO4 came in. I was wondering how much i should start off dosing?

I mixed ~2.25mL of KH2PO4 into a 75mL solution of water. Taken from the ratio suggested in link below "mix 7.2 grams or 1.5 teaspoons or 0.50 tablespoons into 250 ml of water":
http://www.rexgrigg.com/dosing.htm

Given that... it says 1mL of the solution doses "0.53 ppm of PO4 in 10 gallons of water". I have a 40 gallon tank. and my Nitrates showed between 80-100. Does that mean i need to get 10ppm phosphates in the water? that's a lot of dosing? no?

I would first try to lower those nitrate levels (to say 20 ppm or lower, preferably) before dosing your phosphates.