The One Thing No Hydroponic Gardener Tells You About How Often to Change Hydroponic Water

According to Mark, a hydroponic farmer, “You should change your hydroponic water every one to two weeks, but it’s not that simple. Many factors influence change times.” 

I’ve learned through trial and error that system size, plant types, and growth rates impact nutrient usage. 

It’s best to monitor your water quality with an EC meter and observe plant health to know when a fresh change is needed. 

Learning these techniques will save you money on nutrients and boost your harvest.

Key Takeaway

  • For most leafy greens and herbs, change the water every 5-7 days. This is a general guideline as most vegetables in the brassica and allium families do well with water changes at this frequency.
  • For tomatoes, peppers, and cucumbers, change the water every 7-10 days. These fruits and vegetables have higher nutrient and water needs, so the water can be stretched a bit longer before requiring replacement.
  • Signs the water needs changing include fouled smell, cloudy appearance, or signs of nutrient deficiencies in the plants. Ideal pH and EC/PPM levels also rising are indicators it’s time for fresh nutrient solution. Don’t rely solely on timing, use your senses and plant observation too.

Factors That Determine Water Change Frequency

There are several key factors that determine how often you need to change the water in your hydroponic system:

how often to change hydroponic water

Size of the System

System SizeWater Change Frequency
Small (up to 10 gallons)Every 5-7 days
Medium (10-100 gallons)Every 7-14 days
Large (100+ gallons)Every 14-21 days

As someone who has experimented with various system sizes, I’ve found that smaller systems see nutrients depleted quicker due to the lower water volume. Replenishing every 5-7 days keeps things in good balance.

Type of Plants Being Grown

Plant TypeRelative Nutrient UseWater Change Needs
LettuceLow – ModerateEvery 7-10 days
HerbsModerateEvery 7-14 days
TomatoesHighEvery 5-7 days
CannabisVery HighEvery 3-5 days

Some fast-growing plants like tomatoes can use nutrients rapidly, necessitating more frequent water changes to avoid deficiencies. Starting a new system? Stick with greens which are very forgiving.

Rate of Water Loss

Elevated temperatures, strong lighting, and steady airflow in your hydroponic system can increase water evaporation rates (1). 

This indirectly quickens how fast nutrients are diminished. In the summer months, I’ve noticed needing to top up reservoirs every 2-3 days for certain operations.

Time Since Last Change

Give your reservoir a sniff test every few days. Over time, waste buildup causes the water to take on an unpleasant odor. 

You’ll know it’s time for a fresh clean water change when things start to stink! Aiming for biweekly flush outs keeps things clean and smelling fresh.

By understanding these key factors, I hope you now have a better idea of how frequently your specific hydroponic system may require new water Ph adjustments or complete add water refills. 

As always, use your nose, eyes, and an EC meter to guide your schedule. Wishing you bountiful harvests!

General Guidelines for Water Change Frequency

While every system is different, here are some general best practices backed by years of personal experience:

Change Water Every 2 Weeks

Most experts recommend this as the default minimum frequency for a full water refresh (2). This allows for good plant growth with moderate effort.

Top Off Reservoirs Daily

Filling reservoirs as needed helps stabilize water levels, but doesn’t eliminate accumulated waste like a full change does. I top up in the morning and check EC levels daily.

Change When Volume Equals Reservoir

When the total volume you’ve add watered to the reservoir equals its original volume, I change 100%. This ensures nutrients stay balanced.

Watch for Signs of Issues

Foaming, odors, or slick surfaces are signs things have gotten out of hand. Rotting roots from poor ph levels can also necessitate deep cleaning and refreshing all clean water.

Adjust Based on Your System

Every grow is unique. Fine-tune based on factors like reservoir size, plant types grown, ambient grow room temperature and lighting intensity which affect evaporation rates.

My personal system runs well with a change every 10-14 days in winter, 7-10 days in summer. Monitoring with a ph meter also helps maximize harvests while minimizing costs of fresh tap water and nutrients.

With close attention and some trial-and-error, you’ll soon learn your system’s preferences. Happy farming!

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Credit : Joshua Rudd

How to Properly Change Hydroponic Water

A proper water change is crucial for long-term plant growth and optimal root system health. Here are the key steps:

how often to change hydroponic water

Drain Old Water Completely

Disconnect reservoir lid and use a pump or large water container to fully empty old solution. Leaving any behind risks issues down the line.

Rinse with Fresh Water

With the reservoir empty, rinse all inside surfaces 2-3 times with fresh tap water to flush residual nutrients and waste.

Refill with Fresh Solution

Mix a new balanced nutrient solution according to your system’s specs, then refill reservoir to its original water levels.

Match Temperatures

For dwc systems especially, the new solution should be within 5°F of the old to avoid shocking plants from rapid temperature changes (3).

Sanitize Hands and Tools

Before touching new solution, sanitize your hands and any equipment with rubbing alcohol or bleach to guard against pests and diseases.

Paying close attention to detail here prevents contaminating new solution and ensures your plants’ comfort during growth stage transitions. 

I’ve found these basic steps are key to thriving system size-appropriate crops. Happy harvesting!


How often do I need to change the water for different system sizes?

The amount of water, reservoir size and reservoir holds all play a role in determining the ideal frequency for water changes. 

Smaller systems like bucket hydroponics may need changes every 5-7 days while larger reservoir tank systems can often go 10-14 days between fully changes. 

It’s always a good idea to vary based on your specific hydroponics system and factors including plant type and growth rates.

Can topping off the reservoir water replace a full change?

While daily top offs help stabilize water levels, they do not remove the accumulated waste products like a complete flush out does. 

Regular water replacement is still needed to prevent build up of dissolved solids and nutrients absorb. 

Most experts agree full changes every 1-2 weeks are best to maintain ph and ec levels and discourage issues like root rot.

What signs indicate it’s time for a water change?

Some common signs are wilting, yellow or stunted plants grow, foul odors, surface scum, or slime on the sides of the reservoir. 

An increase in ec levels or imbalance in ph level readings from your test kit can also point to the need for fresh water solution. 

It’s always a good idea to keep an eye on your system and notice any signs that a change is overdue.

How do hydroponic gardeners replace the water in systems like deep water culture (DWC)?

For systems like deep water culture (DWC) that sit the plants roots directly in the water solution, the process involves draining the existing water from the reservoir tank using a water pump. 

Then the entire system – from tank to piping to baskets – must be thoroughly rinsed with fresh water 2-3 times to flush out build up.

 Finally, a new balanced nutrient solution can be refilled into the clean system. Maintaining clean water management is especially important for DWC setups.

When should I change nutrient solutions for different types of plants?

Rapidly growing plants like tomatoes, berries and lettuce may require changes every 5-7 days during growth stages while hardier herbs can often go 10-14 days between refreshes. 

Monitoring tools like an EC meter and your eyes will tell you each specific plant type’s ideal water replacement rhythm with experience. 

Varying the schedule based on the crop is key to maximizing yields while minimizing costs.

How can I prevent root rot and other issues?

Some great ways are by changing water solution before levels of dissolved solids get too high ec and ensuring ph levels stay properly balanced with pH-testing. 

Sanitizing surfaces and tools with peroxide or bleach between changes also helps avoid bringing in harmful pathogens. 

Regular fresh water replacements remove build up of waste that can lead to root diseases if left for too long. Preventative maintenance is the best solution for a healthy hydroponic garden.

My hydroponics system has been running for three weeks without a water change – is this okay?

While some larger systems can go up to 3 weeks between changes, it’s generally not recommended to leave the water solution that long without a refresh. 

Nutrient concentrations get high, waste builds up and pH can fluctuate outside the optimal range for plant absorb nutrients. 

Sticking to the weekly or biweekly change schedule will better support your crops’ optimal water needs and ensure optimal plant growth. It’s always a good idea to water regularly.


After many seasons cultivating crops through hydroponics, I’ve found the best route is tailored to your unique system size, plant palette, and environment. 

General guidelines provide a strong starting point, but listening to your gardens’ subtle cues allows fine-tuning the schedule for peak results. 

Don’t be afraid to tweak frequency up or down depending on what you observe. An unhappy wrinkled leaf or musty smell warn that it’s time. 

On the contrary, vibrant green powerhouses may let you stretch to the maximum window between refreshes. 

Most importantly, learn to recognize these signs so you can proactively avoid issues. A little preventative care goes a long way for bountiful, problem-free plant growth. 

Through attentive monitoring with your senses and instruments like an EC meter, you’ll develop a sixth sense for your crops’ individual water change rhythms. 

Before long, changing the solution will become second nature – with healthier, heavier harvests as your reward.

I hope you enjoyed this overview of properly managing water changes in your hydroponic system. Let me know if you have any other questions! Leave a comment below.



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