The How to Database

You can use aquarium water as a mild organic fertilizer by applying it during water changes, but you need to dilute it, use only suitable tanks, and avoid overdoing it. Why aquarium water works Fish waste and uneaten food break down into nitrates plus some phosphorus, potassium and micronutrients, which plants can absorb quickly. The water also carries beneficial bacteria that stimulate soil life, similar to a light compost tea. ​ Nutrient levels are usually low to moderate, so it acts more like a gentle, regular feed than a strong chemical fertilizer. Which aquarium water is safe Use: Freshwater tanks with healthy fish, no recent disease outbreaks. Water that has not been recently treated with medications, algicides, or strong chemical fertilizers; these residues can be unsafe for edible plants and soil microbes. “Dirty” but not foul‑smelling water from routine water changes (slight haze is fine; rotten smell means anaerobic conditions, avoid). Avoid or be cautious with: Saltwater or ...