In hydroponics, there’s no soil to act as a buffer. The roots live entirely in the nutrient solution — that’s their whole world. And just like in an aquarium, if that “world” starts to go bad, the inhabitants suffer.
The question “how often should I change my water?” pops up constantly on grower forums. There’s no one-size-fits-all answer, but there are solid principles that keep your system clean and your plants thriving.
Why Change the Water at All?
- Salt buildup – Over time, minerals and nutrients accumulate, throwing off the intended balance.
- pH and EC drift – Plants absorb some nutrients faster than others, leading to imbalances.
- Pathogen risk – Stagnant, “tired” water invites algae, bacteria, and fungal growth.
- Oxygen freshness – The older the solution, the less dissolved oxygen it tends to hold, and roots notice.
The General Rule – “Once a Week”
For most DWC (Deep Water Culture) and NFT (Nutrient Film Technique) setups, the rule of thumb is a full water change every 7 days.
But — and here’s where grower experience comes in — this is just a starting point.
When to Change More Frequently
- During flowering – Plants drink and feed faster, and evaporation concentrates the solution.
- In high temperatures – Warm water accelerates bacteria and algae growth.
- After adding supplements – Especially organic boosters or amino acids, which can spoil in the tank.
- If water changes color or smell – That’s your first red flag something’s wrong.
When You Can Wait Longer
- In well-chilled systems (18–20°C) with strong circulation and aeration.
- During early vegetative growth at low EC (<1.0).
- If you’re topping up daily and adjusting pH/EC as needed.
Best Practices for Changing Water
- Prepare the new solution in advance – Ideally the day before, so temperature and pH stabilize.
- Avoid “shock” – Keep the temperature difference between old and new water minimal.
- Clean the reservoir – Rinse with warm water each time; disinfect every few weeks with a safe cleaning agent.
- Monitor pH and EC daily – These numbers often tell you more than a calendar ever could.
What About Recirculating Systems (RDWC)?
Large recirculating systems often use partial changes — replacing 30–50% of the water every few days and doing a full change every 2 weeks.
Still, many experienced growers prefer a weekly full change anyway — clean water means clean roots.
A Little Trick from Old-School Growers
Some keep a separate buffer tank of aerated RO (reverse osmosis) water on standby. This lets them top up fresh water daily, so full changes become less urgent — though still important.
Conclusion
In hydroponics, water isn’t just a carrier for nutrients — it is the plant’s environment. The “once-a-week” rule works for most setups, but the best growers adjust based on pH, EC, temperature, and root health. In hydro, as in life, prevention beats cure every time.
