If you have an aquarium in your home, you might be asking yourself, “is aquarium water good for plants?”, “Can I use it to water the plants”? The short answer is yes, yes you can, not always, but generally yes.
Part of owning a fish tank and having fish is regularly changing the water in your tank. Unless you have some high-quality filtration system in place, which will remove the need to change the water as frequently.
Before going into this further, we should note you can only use aquarium water if you have freshwater fish. Under no circumstances should you use saltwater to irrigate your plants. If you have saltwater fish in your tank, you can’t use fish tank water for watering.
If you notice disease on fish and plants or dead fish in the tank, avoid using the water for your plants.
As various chemicals are often added to the fish tank to keep flora and fauna happy, we only recommend using the aquarium water for watering your houseplants (or outdoor ornamental plants) and never plants that are meant for consumption.
If you are using algicide (and we would not suggest you do), you shouldn’t use the water for your plants.
Assuming you have freshwater in your aquarium, the water from the tank is wonderful for your plants. As fish do their business (number 2) and food and flora decomposing, this all adds to the water becoming rich with nutrients and beneficial bacteria. Your plants require those to thrive.
Is aquarium water good for plants?
Think of aquarium water for your houseplants as manure with garden plants—a wonderful natural fertilizer.
As the aquarium water becomes dirtier, it is becoming richer. It gets nitrogen, potassium, and many other nutrients you normally find in store-bought fertilizers for your plants. So you can see why plants will appreciate it.
All the harmful minerals you would find in tap water are also long gone or heavily decreased, depending on the mineral.
How do you use it?
That depends on the size of the tank and your needs. If you have a big tank, you can use aquarium water as the only means of watering. Take the water from the tank as you need it and water your plants. You can scoop it with a clean watering can or cup. Don’t forget to replace the water too.
If you regularly do partial water changes, that water is good for watering the plants, too. Stirring the water and sand/stones too much as you change will make it murky. This means more nutrients (fish poop and all) gets mixed in the water. You might need to dilute it a little before watering.
Changing all of the water? If you are changing all the water in your tank, chances are it is packed full of nutrients, even more, than your plants need, so you can dilute it before watering the plants with it.
Can Fish Tank Water Replace Fertilizer?
Yes and no. This all comes down to quantity. Quantity of water available and quantity of plants. And the time between how often you change your water – the longer the water is in the tank, the more nutrients. If you change the water very often, it won’t have the amount of nutrients your plants require or would get with a commercially available fertilizer. Want your plants to trhive? Add store-bought (or homemade) fertilizer.
If you have a large aquarium and a couple of plants, then yes, you can use the aquarium water to water your plants without the need to ever fertilize them.
If you change aquarium water very often, the water won’t necessarily be rich enough with nutrients to have the same effect as commercially available fertilizers.
Can you Use Aquarium Water and Fertilizers for Plants?
Yes and no. As previously mentioned, this depends on the quantity and time. If your fish tank water is full of nutrients, adding fertilizer on top of that will harm your plants as they will be overfed.
If your fish tank water isn’t packed with nutrients, or you have to dilute it enough in order to water all your plants, adding fertilizer will benefit the plants.
It’s a trial and error thing, as it is with all things with plant care. Observe your plants and do what makes them happy.