Liquid fertilizer or root tabs?
Plants that take food from the water need a liquid: stem plants, floating plants, and mosses and ferns tied to wood. Plants with big roots in the substrate need root tabs: Amazon swords, crypts, vallisneria and lilies. A tank with both kinds uses both. More on which nutrient does what in the fertilizer guide.
Why the doses differ so much
The products are not the same strength or the same recipe. API Leaf Zone is mostly iron and potassium. Seachem Flourish is trace elements and minerals with almost no phosphorus (Seachem gives it as under 0.01 percent). Tropica Premium Nutrition leaves out nitrogen and phosphorus on purpose, for tanks where fish waste supplies them. Easy Green is an all-in-one that includes nitrogen, so it raises your nitrate reading. A milliliter of one is not a milliliter of another, so dose each by its own label and never mix two all-in-ones at full dose.
When to adjust
Start at the label dose, or below it in a tank with weak light and few plants, and change one thing at a time over a few weeks. New leaves coming in pale or yellow point to too little; algae on the glass and leaves while the plants stall points to more food or light than the plants can use. A nitrate test helps: with an all-in-one, nitrate climbing past 40 ppm between water changes means you are adding more than the plants take up. Read the leaves · How long to run the light
Shrimp and snails
Seachem says Flourish is safe with shrimp: it carries copper, but only the trace amount that plants, and shrimp too, need. Copper harms shrimp and snails in larger amounts, so the risk starts with overdosing any fertilizer. In a shrimp tank keep to the label dose or below it. Plants for a shrimp tank