I do ten drops a gal and still have gnats this is 4x weaker than gnatrol. So tbh if u can get the water dispersable granular do it . And do not get dipel its for catarpillar not gnats get the wdg. Its more expensive but u use less imo, 2 or 3 drops per gal is to weak like most say. For best resuls add to oxygenated res and keep water slightly warm. It should grow in a few days or so possibly depending on o2 and TEMP of res.