For a macro fertilizer you need to add potassium, calcium magnesium sulfur. For micros you need chlorine, iron, Boron, Manganese, zinc, Copper, nickel, molybdenum.
You also need a fertilizer calculator. I use:
For the macros you can use calcium sulfate, magnesium sulfate and these will supply the needed sulfur. for calcium and magnesium you want about a 3 to 1 ratio (3 parts ca to 1 part Mg). Dose this during your once weekly water change and add enough to increase your GH to 2 degrees GH. For potassium you can use Potassium chloride which will also apply the need chlorine. Many other people use K2SO4 for potassium but you don't need the sulfur sine your Ca and Mg has it. For potassium you want 1 part potassium to 1 part nitrate. So if you have 10ppm nitrate I would add about 10ppm KCl. That should address all your macros.
(phosphates because I have a BBA bloom in my tank and I read somewhere that it is connected to phosphate levels) but has other required elements for my plants.
High levels of phosphate, and nitrate, were once thought to cause algae but it has been shown many times that plant nutrient deficiencies cause most algae issues (not PO4, NO3, NH3) . I you have all the nutrients your plants need algae tends to grow slowly and plants will grow faster than the algae. Having sufficient macros might be all you need. You should use test kits to measure nitrogen and phosphate levels. Ideally you want nitrate levels between 5ppm and 20ppm with phosphate levels at about 1ppm. if you need to add these use potassium nitrate KNO3, and Potassium mono phosphate KH2PO4.
If just dosing macros doesn't solve the problem you will need micro fertilizer. Most people buy these but if you need to make your own you may want to look at this thread:
All of the ingredients can be hound on line ate Amazon.com, Loudwolf.com, Ebay and other sites. On wikipedia.org you can find information on each chemical used in fertilizers and general information on plant nutrition:http://https://en.wikipedia.org/wiki/Plant_nutrition