So my plants have potassium deficiency, what should I buy?
If you are sure your tank has enough nitrates and phosphates you can buy API Leaf Zone or Tetra Flora Pride. They only have potassium and iron with no phosphates or nitrates added. If you do not like the added iron you can buy Flourish Potassium or dry Potassium Sulfate. I take it you are catching up to add potassium without risking an algae outbreak due to excessive nitrate or phosphate?
Idk. Will Flouish Comprehensive give enough potassium so that I don't have to buy specifically potassium?
Yes it would and keep up with the water changes.
Ah thanks. So when should I buy potassium over Flourish? Thanks