With traditional horticulture, the quality of the soil is an important factor. With hydroponics, it is the quality of the water. Sure, you'll likely be adding water to your hydroponics system periodically, but you will also need to change it periodically. How often you need to change the water can vary slightly because of different setups, but there are a few general rules you need to follow.
The Role of Water in Hydroponics
Water in a hydroponic system does more than just keep plants hydrated. It carries all the nutrients they need to grow and thrive. Over time, as plants absorb these nutrients, the balance of the solution shifts. Some nutrients get depleted, while others build up to levels that may no longer be good for your plants. This is why regular water changes are essential—they help maintain a stable environment where plants can continue to grow without stress.
How Often Should You Change the Water?
A full water change every two to three weeks is a good rule of thumb. This ensures your plants always have access to fresh, well-balanced nutrients. However, several factors can influence how often you should change it.
The size of your system plays a big role. Smaller hydroponic setups can see nutrients used up quickly, so you might need to change the water out more frequently. However, the growth stage of your plants also needs to be considered. Young plants consume fewer nutrients, so you can often go a little longer between changes. But once they hit their rapid growth phase, nutrient uptake speeds up, and you’ll likely need to change the water more frequently to keep up with demand.
Environmental conditions can also play a part. Warmer temperatures can lead to faster evaporation and higher nutrient concentrations in the water, which means you may need to top up or refresh the solution sooner than expected.
Do You Need to Change All the Water at Once?
Not necessarily. Between full water changes, you’ll need to top up your system to replace water lost to evaporation and plant uptake. But topping up isn’t the same as changing the water. As a general rule, once you’ve added back the equivalent of your system’s full water volume, it’s time for a complete change.
For example, if your reservoir holds 50 litres and over time you’ve topped up with another 50 litres, it means the original water has been diluted enough that it’s time for a fresh batch.
Signs That It's Time for a Water Change
Even if you’re following a set schedule, it’s important to pay attention to your plants and water quality. Sometimes a system needs a water change sooner than expected.
One of the first signs is pH instability. If the pH is fluctuating more than usual and you find yourself constantly adjusting it, your solution may be unbalanced, and a full water change could help reset things.
If you notice algae growth, especially in exposed areas of your system, it’s a sign that conditions are starting to favour unwanted organisms. While proper light control and system cleanliness help prevent this, a fresh batch of water can clear out excess nutrients that algae feed on.
Water that starts to smell unpleasant is a red flag. A healthy hydroponic system shouldn’t have a strong odour. If you notice a musty or sour smell, it could indicate bacteria or root rot, and an immediate water change is necessary.
Lastly, if plant growth slows down unexpectedly, even though everything else seems normal, it might be due to an imbalance in the nutrient solution. A fresh mix can help bring things back on track.
How to Change the Water in Your System
When it’s time for a water change, follow these simple steps:
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Prepare fresh nutrient solution – Before draining the old water, mix a new batch according to your system’s needs, checking that the pH and nutrient levels are correct.
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Remove plants if necessary – In smaller systems, you might need to temporarily lift plants out to access the reservoir. Be gentle with the roots.
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Drain the old water – Empty the reservoir completely to prevent nutrient buildup. If possible, rinse the tank and pipes to remove any residue. If you have to use cleaning solutions, make sure they are plant friendly.
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Refill with fresh solution – Slowly add the new mix back in, ensuring it circulates properly before placing plants back in position.
Keeping Your Water Clean Between Changes
While regular water changes are important, good system maintenance will help extend the life of your nutrient solution and keep things running smoothly.
Make sure to monitor pH and nutrient levels daily. If you catch imbalances early, you can correct them before they cause bigger issues.
Keeping water temperature in check is also key. Most hydroponic plants do best when the water stays between 18–25°C. Warmer water can lead to bacterial growth and oxygen depletion, which stresses the plants.
If possible, use filtered or dechlorinated water. Tap water often contains minerals and chemicals that can build up in your system over time, affecting nutrient balance.
Staying on top of water changes is one of the most important things you can do to keep your hydroponic plants healthy. While every system is different, changing the water every two to three weeks is a solid starting point. And—naturally—watch for signs that your plants or water quality might need attention sooner, and always keep an eye on pH, temperature, and nutrient levels.
With the right approach, you’ll create a thriving hydroponic setup that produces strong, healthy plants with minimal stress. And if you ever need expert advice or high-quality hydroponic supplies, A-Grade Hydroponics has you covered.
