Is Old, Dirty, Used Fish Tank Water Good For Plants?

A lot of people don’t know that fish tank water can be used to help plants grow better.

Fish tank water is often seen as a waste product that needs to be disposed of, but it can actually be used to help your plants grow stronger and healthier.

By using fish tank water in your garden or house plants, you can help them thrive without having to spend extra money on plant food or fertilizers.

Is Fish Tank Water Good For Plants?

Although “dirty” fish tank water is harmful to fish, it is great for plants! It’s full of beneficial bacteria and trace elements that will stimulate lush, healthy plants. Aquarium water is great to irrigate plants as it has some of the same minerals found in many store-bought fertilizers.

In the article below we look deeper and answer the question of whether or not fish tank water is good for plants?

The answer depends on a few things like water quality and the types of plants you intend to grow.

We’ll get into some of the answers below.


What Do You Do With Old Fish Tank Water?

That depends a lot on the water itself. Some of the factors that may determine what you can do with your aquarium water are:

  1. How frequently you change your aquarium water. If you change it regularly (actual frequency depends on the size), it will most likely only contain a limited amount of nitrogen compounds.
  2. What kind of fish you have. Some species are messier than the others, even if the biomass is equal. Goldfish, for example, are very dirty. Good for plants, bad for your aquarium.
  3. Whether your aquarium water is hard or soft. If it’s hard, it may not be of much use.

What do you do with the dirty, used water, apart from dumping it down the drain?

The most common answer to that is: Use it for watering your plants.

If you have a garden at home and are also a fish keeper, you can create a beneficial cycle for both activities. You regularly change the water in the aquarium, and instead of discarding it, you can use it to water the plants in your garden.

But that works only if the dirty, aquarium water is beneficial for plants. It usually is, and one of the most prominent examples of this are aquaponic systems. These are mutually beneficial, symbiotic systems that combine fish and plants.

The ammonia build up in the aquariums is bad for fish, but it’s suitable for plants. So plants are grown in a way that they benefit from the ammonia, and since they absorb it, the aquariums become cleaner and healthier for the fish. It’s akin to using manure as a natural fertilizer.

Another way you can use dirty aquarium water is to set up a new tank, especially a planted fish tank. Used aquarium water can help establish the beneficial bacteria and jump-start your fish tanks cycle.

It also has the right nutrients, useful bacteria, and other helpful chemicals to keep aquarium plants healthy. But it can also be bad for your fish in the new tank. A smart idea would be to check nitrogen levels before using it.

How Does Fish Waste Help Plants Grow?

The waste that your fishy friends create in the aquarium breaks down into ammonia, which eventually converts into nitrate. If enough nitrates accumulate in the tank, it can make your fish sick and possibly even kill them. This is why most tanks come with a filter, and even then, it’s recommended that you also change the water in the tank periodically.

However, this ammonia (and nitrate) is beneficial for plant growth. The aquarium plants benefit from the fish poop.

But it’s not just useful for plants in your aquarium. Used aquarium water, which contains ammonia and other harmful chemicals, produced by the break down of uneaten fish food in the tank, can also help other plants grow.

It’s all-natural fertilizer full of useful nutrients that can enrich the soil and expedite plant growth.

Benefits Of Using Fish Tank Water For Plants?

Here are a few quick benefits:

  1. Your water isn’t wasted. Instead, it’s effectively recycled.
  2. You save money on both fertilizer and water. If clean water is an expensive commodity where you live, using aquarium water is a financially smarter choice.
  3. It’s a natural fertilizer. That’s a huge plus for people who are into organic plants and gardening without using chemical fertilizers; used aquarium water is a greener alternative.
  4. It can be helpful for plants in another tank as well, but only if it isn’t too contaminated for the fishes there.

Is Fish Tank Water Good For Indoor Plants (Houseplants)

The answer to the question depends upon what kind of indoor plants or houseplants you have, and if you use any chemicals to keep the water in your aquarium well-balanced.

For example;

If you put any additives in the water, you may want to keep it only for ornamental plants and not for watering food-producing house plants.

Also, if you spend too much time between water changes, you may want to dilute it for your delicate houseplants. Your indoor flowering plants may like water from aquariums before they start blooming because, at that stage, they need more phosphate than nitrates.

There are some indoor plants you can grow directly in your aquarium, like Golden Pothos, Climbing Fig, and Lucky Bamboo. A smart idea is watering only those of your indoor plants that need fertilizers with used water.

Is Fish Tank Water Good For Your Garden?

Garden plants, especially hardy garden plants (like Begonia, Tickseed, and Coneflower), are likely to thrive in such nitrate-rich water. One main problem with watering your garden plants with used aquarium water would be the quantity. Unless you have enough aquariums, you might need to use fertilizers in addition to the used water. But if you put chemicals in your aquariums, you shouldn’t be watering any delicate garden plants with it.

Is Fish Tank Water Good For Vegetable Plants?

Using water from your fish tank for your vegetable plants is fine, as long as you don’t add any additives to it to maintain parameters. If you put chemicals in to lower the pH, or even as medication for sick fish, the water might not be desirable for your vegetable plants.

That said, aquaponic setups focus on vegetables all the time. But that’s mostly because it’s completely natural, without any chemical additives, and creates a helpful cycle.

Is Fish Tank Water Good For Tomatoes

Most tomato species are popular in aquaponics setups and seem to grow well and thrive on the waste produced by the fish, and other nutrients that they find in the aquariums.

The water from your aquariums will be beneficial for tomatoes in the garden as long as you haven’t dosed it with certain chemicals. However, the plant’s health will depend upon other factors like sunlight and soil quality.

Jack Dempsey
Follow Me