How Often Should I Change My Hydroponics Water?

The condition of the water becomes of paramount importance for the healthy growth and development of the plant in hydroponics. When to change the water and how should be done in a hydroponic system is a problem that every beginner and veteran hydroponic grower has experienced.

In general water in hydroponic should be added every 2-3 days or more often. This is to compensate the lost water through evaporation, transpiration, or plant water consumption. A full water change should be done once the total water topped off is equal to the maximum water capacity the system can hold

The question of when and how to change the water in your system is a simple answer but underlying reasons are much more complex. This article will best explain for the layman the how’s, the why’s, and the whats of changing your hydroponics water.

What’s The Purpose of Changing the Water?

Changing the water in your hydroponics system – has two functions: 1) controlling the water nutrient, pH, mineral and microorganism as well as 2) preventing the formation of biofilms functions

Controlling The Water

The biggest and most obvious advantage of changing your water in hydroponics is to know exactly what’s in the water. Indeed, over time, the water you added tends to change its chemical characteristics (nutrients, content, pH and more) making it less suitable for growing plants.

Hydroponics is all about providing water with controlled levels of EC (electric conductivity), pH (acidity), nutrients, and mineral salts, if any.

Hydroponics water mixed with nutrients have varied levels of EC, pH, nutrients, minerals, and microorganisms become more difficult to regulate later on as time passes due to the how these factors interact with one another. As such, changing the water lets you have a blank canvas to work with.

Preventing Biofilm Accumulation

Another important reason to change water in hydroponics is to avoid the formation of biofilm accumulation. This is the results of growth and buildup of microorganisms on a surface (imagine the green algae forming on the surface of a pond).

The presence of biofilm can possibly lead to phytopathogen infections in plants, ranging from fungi, to parasites, to viruses. Thick biofilm accumulation may possibly clog the pipes and drains in a hydroponics system, making water recirculation less efficient and nutrient distribution less effective.

Changing the water can help prevent biofilm accumulation and allows for the cleaning of the system.

Two Types of Water Change

There are two types of water change in hydroponics and both cannot exist without the other.

Topping Off

Topping off is exactly what it sounds like. Rather than replacing all of the water out right, you merely refill the water lost due to evaporation, transpiration, and the plant’s water consumption. Likewise, more plants or growing plants which require more water will increase water consumption.

To top-off a hydroponic system it is necessary toadd a bit of water every 2-3 days or more often. It’s important to keep track of how much the volume of the water is topped off because it will indicate when a full water change is due.

Make sure to keep a record of how water is added!

Full Water Change

When the total volume topped off is equal to the total volume capacity of the reservoir, then it is time to change the entire water reservoir. A full change usually takes around 1-3 weeks depending on the size of the system or the quantity and nature of the plants grown.

A full change can be done manually by simply draining the reservoir or throwing out its contents. This can also be done automatically through the use of pumps to pull in water from reservoir to another container.

Upon draining the old water, you can take this time to clean and scrub your hydroponics system with a simple scrub. Apply diluted 35% hydrogen peroxide with water or diluted bleach and scrub away. Try to get rid of the biofilm accumulation and make sure to unsettle the minerals or particles that may have deposited to the bottom of the reservoir.

After cleaning, you can now add water with stock nutrient solution and bring plants back into the system.

What Can Go Wrong in Changing the Water?

An improper water change without taking into account the pH, EC, and the nutrient content of the water may harm your plants.

Changing The Too Early

Doing a full water change too early may cause the plants to enter root shock because the plants did not gradually grow accustomed to the sudden change in the hydroponic water’s content.

This is why topping off is important. Topping off allows for the gradual and incremental changes in the hydroponics water allows the plants to survive.

Changing The Water Too Late

A practical concern of changing the water too late is that plants may intake more of a specific nutrient than all the other nutrients causing the nutrient content of the solution to be out of balance. This could lead to the hydroponics water to be deficient or excessive in nutrients or other factors.

As stated previously, changing the water too late may introduce harmful microorganisms which may harm the plant. This is further exacerbated when light is allowed to penetrate the reservoir, inducing the accumulation of biofilm.

Tools To Monitor EC and pH

Throughout the entire process of growing hydroponically, it’s important to observe the EC and pH levels. This is a fact regardless if you’re topping off or doing a full water change.

The EC measures the mineral salts and nutrients in your system. On the other hand, pH measures the power of hydrogen or how acid or basic the water in your system is.

The optimal number for EC should be between 1.2-2.0. The optimal pH level for most plants is from 5.5 to 6.0. The optimal numbers vary depending on the plant but these are the optimal levels which are generally held in the growing community.

These can be easily measured by thru easily available and simple to use EC/pH meters. Recommended options are the Bluelab Nutrient Meter and the Hanna Instruments pH Pen which can be found here and here on Amazon, respectively.

With these tools, deficiencies and abnormalities in the system can be remedied by taking the proper preventive actions. There’s no need to wait for something to go wrong before acting.

What To Do With The Hydroponic Wastewater?

Hydroponics water rich with nutrients still has its uses, provided that you retained the hydroponics wastewater. Add more water into the discarded hydroponics wastewater and thoroughly mix to dilute the nutrients.

From this, you can use the waste to either water your indoor and outdoor plants and the soil they are planted in. Even diluted hydroponic wastewater is still nutrient rich and would be beneficial to plant growth and development.

Alternatively, you can toss it out the sink or a canal.

Can Hydroponic Plants Be Overwatered or Drown?

In hydroponic systems it is possible to overwater or even drown a plant. This happens due to the lack of an insufficient level of oxygen. A fully working hydroponic system needs to guarantee some specific level of O2 in the water.

Plants “breathe” through their roots. Aeration of the roots is important to both soil and hydroponic cultivation. Without oxygen, anaerobic respiration occurs which produces toxic by-products that kill plant cells.

This usually occurs when roots are exposed to overwatered conditions. Worse, fungus may grow due to these damp conditions. Both conditions result in root rot which is detrimental to the growth and development of the plant. Root rot can be identified by dark roots as opposed to the white roots found in healthy plants.

This is why soil aeration is an important consideration in selection soil for soil cultivation. The same can be said for hydroponics but this is circumvented through more innovative means.

The means are similar in principle among all the hydroponics systems in existence. The roots are only partially submerged in water. Some roots are in the growing medium in the grow tray or are allowed to dangle in the empty space between the grow tray and the surface of the water for the sole purpose of taking in oxygen.

In conjunction, airstones and air pumps are employed to ensure that there is dissolved oxygen in the hydroponic system to ensure that even the fully submerged roots have access to oxygen.


  1. Changing the water in hydroponics is a normal part of the process.
  2. Topping off should be done every 2-3 days. Keep a record of the volume of topped off water since this will dictate when it’s time to do a full water change.
  3. A full water change occurs every 1-3 weeks, depending on the size of the system, and the quantity and nature of the plants grown. is part of the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites like mine to earn advertising fees by promoting good quality products. I may receive a small commission when you buy through links on my website.


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