How Often Should I Change Water In A Hydroponic System To Get Best Results

With artificial light and growing conditions, the only natural resource that hydroponic plants have is water.

Now, plants in a hydroponics system must be able to get the nutrients from this water in the most efficient way.

For that, you need a detailed answer to how often should I change water in a hydroponic system. And here, you will get that answer, so keep on reading.

Like typical plants use soil as a growing medium, hydroponics use water. Soil develops a lot of different microbes which are mostly beneficial for the plant.

However, any such microbes are harmful to hydroponic plants and hence are unwelcome in the hydroponic system.

To ensure that no bacteria or microbes develop, we regularly need to change the hydroponic water, but first, we need to know how to change it. Let’s see into that

How To Change Water In Hydroponic Systems

Water as a growing medium is home to plenty of nutrients and compounds, which are otherwise provided to the plant via soil.

These compounds besides strengthening the plant also make ideal conditions for the formation of microbes. 

When we talk about changing hydroponic water, it is not due to the depletion of nutrients. For that, we just add a hydroponic nutrient solution.

Here, it is due to microscopic gunk and microbes that might affect the plants adapted to grow in perfectly clean and hygienic conditions. 

There are two methods to change the water in the hydroponic systems, topping off and complete change of the water. 

Hydroponic water tank to depict the amount of water for people asking the question how often should I change water in a hydroponic system
Hydroponic water

Topping off

Plants drink water too, not literally, but yes they do. They do this through roots and this water travels through the whole plant body to the leaves.

In the leaves, this water evaporation from the leaves’ pores through transpiration (think of this as plant perspiration).

This causes a small but gradual decline in water in the hydroponic tank.

Adding an equal amount of freshwater as transpired from the tank is called topping off. You can add this water anytime you see the water level lower than full. However, it is better to keep a schedule. An average of 2–3 days is the optimum frequency for topping off unless the tank is too small. 

This method saves time, cost, and water; plus, it’s really simple. However, when problems related to pH, microbes, or nutrient accumulation occur, topping off does not help much. Moreover, after topping off too many times, the substances start getting accumulated in the tank.

To solve these complications, another method is used.  

Complete change

In complete change, as the name suggests, we change the whole water in the system.

This saves up the effort of keeping account of how much water to add and when to add. However, what this method does not save is water.

So, will not be a good approach if you do not like to waste much water. 

But why completely change the water when topping off works? Well, topping off does not always work. In cases when some issues with water arise, like abnormal pH, toxicity, nutrient accumulation, or pathogen formation.

The average time to change the water completely for an average-sized tank is 15–20 days unless there is some issue, in which case the water is to be changed immediately.

When Do I Need To Do A Complete Water Change?

As discussed earlier, some issues cannot be solved by topping off. What are those issues? Let’s look into those in detail

Due to pH changes

pH is the measure of the acidity or basicity of water. When the pH starts fluctuating too much due to the accumulation of ions from different compounds, it affects the mineral absorption ability of the roots. In this situation, the water needs to be replaced entirely. 

Normally you’d think that neutral pH water would be good, but nope, not in the case of plants.

Though the specific ideal pH changes from plant to plant, the general figure is somewhere between 5.5-6 which is slightly acidic. 

However, if you’re conscious about the specialized needs of your plants, then here’s the chart that tells you about the ideal pH range for hydroponic water of some commonly grown hydroponics. 

pH chart of some commonly grown hydroponic plants
pH table for hydroponic plants

Due to microbe growth

Most of the nutrient solutions we use in a hydroponic system are synthetic. Despite that, if their nutrient contents get too concentrated, they provide good enough conditions for microbes to develop. 

There are ways to kill the microbes and sterilize the water, but it’s not worth the effort.

Moreover, such procedures might or might not sit right with the plant. So the only viable way is to replace it with fresh water after a set number of days. 

Water getting muddy due to microbial growth
Hydroponic water

Hit And Trial Testing  

Hydroponics is not something that you either know or not, it is more of a learning process.

And like all learning journeys, you make a lot of mistakes in this journey too, especially if you are just starting out. 

The good thing is that you learn from every mistake. Hit and trial testing is just a fancy phrase for learning from mistakes. 

When such mistakes relate to the hydroponic water or its contents, then treating it or topping off is a risky business.

Therefore, whenever you try some new nutrient solution or pH range, look for even the slight expression of symptoms of stress in the plant.

If any, then immediately replace the water with fresh one and try something different now, until your plant finds it good. 

Some Important Points:

  • It is better to take the water for hydroponics from the same source. If the water source is different, then it also has different levels of pH, ions, dissolved salts, and electrolytes. These changes can cause transplant shock to the plant, which might then show disease symptoms. 
  • While performing a complete change of water, always clean the tank with clean scrubbers and some non-toxic solution to get rid of any potential microbe infestation or contents of the nutrient solution.
  • Always use pH-balanced water when doing the hydroponic water change, to avoid any transplant shock to the plant, that might affect the plant growth.
  • Allow a small amount of fresh water to stay in the even during the complete water change process, as transpiration in plants never stop, and hence nor should their absorption of water.

So, the simplest answer to the beginners’ question of how often should I change the water in a hydroponic system is ‘not that often’.

Just top it off, unless you face any of the above-explained situations. Now with everything clear regarding the hydroponic water tank, set up your hydroponic system, so that your plants can drink and transpire from the fresh supply of water as much as they want.


Can I just treat the used water and reuse it instead of wasting it?

If you can afford the cost and effort of treating it, then sure, go for it. But it is generally not recommended, as just using fresh water is far more economical and easy. 

Do plants confuse different amounts of water during different stages of growth? 

Yes, as the plant grows more and more leaves, it transpires more. However, your check when to add more water is not based on its growth stage. It is based on its level in the hydroponic tank, so just keep a look at it. 

Are there any physical signs that tell me it’s time to change the water?

Though there are such physical signs like, visible microbial growth, change in water color, and symptoms on plants, etc., these signs often appear when the damage is irreversible. So, it’s better to just regularly change the water without waiting for such signs. 

Can I add nutrients directly to the water in my hydroponic system without changing it?

While topping off, yes. But when you have to change the water completely, then adding it after changing it is the best decision.

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