If you own a freshwater fish tank, then you're already aware of the need to change water regularly to keep your fish healthy, but what few people know is that the water can be recycled for plants. Using fish water to water plants can add an extra shot of nutrients to your plants' soil because of the fish waste. Because the fish waste is already in liquid form, it's easy to apply to any plant.
Plan to water houseplants and/or outdoor plants with fish water in place of, rather than in addition to, a regular watering, or you may drown your plants. Try to plan so that the two events occur together.
Put a small bucket or large cup into the fish water and fill it with water. Pour the water into your watering can, but take care to only fill it as full as you can easily carry.
Water your plants along the soil level at the base of the plant; avoid wetting the foliage and leaves. Add water to the plants until there is no fish water left or your plants are well watered.
Water your plants with fish water as often as once a month, using regular watering as needed to keep the plants healthy between applications of fish water.