This is my best guess. I don't use Greg Watson products.
Plantex - Comparable to Seachem Flourish. Micronutrient trace element mix. (I dose Seachem Flourish twice per week)
KN03 Potassium Nitrate - Comparable to Seachem Nitrogen. Shouldn't really be needed in a tank with full stock of fish. Increases Nitrate.
KH2P04 Mono Potassium Phosphate - Comparable to Seachem Phosphate. Again shouldn't really be needed in a tank with full load of fish. Increases Phosphate.
K2S04 Potassium Sulfate -Comparable to Seachem Potassium. Increases Potassium. (I dose Seachem Potassium three times per week.)
Iron Chelate - Comparable to Seachem Iron. Increases Iron. (I dose Seachem Iron every day.)
Magnesium Sulfate - Should be mixed with an equal amount of Calcium Chloride to raise gH. Comparable to Kent Botanica gH+. (I check gH using a test strip after a water change, then add as needed to get gH to desired level.)
I feel the Greg Watson pages should include this basic info for newb's. Even someone (like me) who is used to using products from "Aquarium" companies (like Seachem, Kent, etc.) would be more turned to using his products if information like this was presented on his site. Preferably in the store section's product description pages.
Those articles are great info, but for someone staring at the Greg Watson store's product page and is clicking the description links, trying to decide what to purchase, the articles aren't the best help.