Water Management in Aquaponics Basics

by Roger Loper

Do I need to change the water in aquaponics?

Of course! This is one of the most common and important questions for those new to aquaponics.

The short answer is: No, you do not need to perform regular, complete water changes in a well-balanced aquaponics system. This is one of the key advantages it has over traditional aquaculture (fish farming) or hydroponics.

However, the longer and more accurate answer is that you will need to top off water and occasionally may need to do a partial water change for specific reasons.

Let's break down the details.

Why You Don’t, Do Complete Water Changes

In a traditional fish tank, fish waste (ammonia) builds up and becomes toxic. You must do regular water changes to dilute these toxins.

In aquaponics, you have a natural filtration system:

  1. Fish produce ammonia-rich waste.
  2. Beneficial bacteria (Nitrosomonas) convert the ammonia into nitrites.
  3. Other beneficial bacteria (Nitrobacter) convert the nitrites into nitrates.
  4. Plants absorb nitrates, which is an excellent fertilizer for them.

This cycle cleans the water for the fish and feeds the plants. In a perfectly balanced system, the only inputs are fish food and minerals that your plants need, and the only outputs are plant growth and fish growth. You are not constantly removing waste; you are recycling it.

Why You Will Need to Add Water (Top Off)

Water will leave your system through:

  • Evaporation: Especially in warm climates or greenhouses.
  • Transpiration: Plants absorb water and release it into the air through their leaves.
  • "Blow-down": A small amount of water is lost from splashing or system maintenance.

You will need to regularly top off your system with fresh, dechlorinated, pH balanced water to make up for this loss. This is the most common form of "water addition."

When You Might Need a Partial Water Change

Even in a well-managed system, certain compounds can build up over time to levels that are harmful to fish or inhibit plant growth. This is when a partial water change (e.g., 10-25%) is a good idea. Try to save your water for topping off later.

Reasons for a partial water change include:

  1. Accumulation of Solids: If your system doesn't have adequate mechanical filtration (e.g., a swirl filter or clarifier), solid waste can break down and cause a buildup of organic matter, leading to low oxygen zones and harmful bacteria.
  2. Build-up of Non-Nitrate Compounds: The nitrogen cycle manages ammonia, nitrites, and nitrates. However, other elements like salts, metals, and hormones (from fish waste) can accumulate over many months and become toxic. A partial water change helps dilute these.
  3. Correcting a Chemistry Mistake: If you accidentally add something to the system that throws the pH or nutrient levels wildly out of balance, a partial water change can be the fastest way to correct it.
  4. Disease Treatment: If your fish gets a disease that requires medication, you may need to isolate them for treatment. Afterward, you might do a partial water change to remove any residual medication before re-introducing them to the main system. It is highly recommended that you move affected fish to a stand alone hospital tank for treatment as most medications are not meant for use where it gets into the human food chain.

Key Takeaways & Best Practices

  • No Regular Complete Changes: Never dump and replace all your water. This will kill the beneficial bacteria that are the heart of your system, causing it to crash.
  • Top Off Frequently: Always use water that has been dechlorinated and pH balanced (e.g., left to sit for 24 hours or treated with a dechlorinator). Chlorine will kill your beneficial bacteria.
  • Monitor Your System: Test your water regularly (ammonia, nitrite, nitrate, pH). This will tell you more about the health of your system than any calendar schedule.
  • Partial Changes are a Tool: Think of a 10-20% water change as a corrective or preventive maintenance task, not a regular chore. You might do it seasonally or if your water tests indicate a problem.
  • Filtration is Key: A good filtration system (mechanical and biological) will drastically reduce the need for even partial water changes.

In summary: Stop thinking like an aquarist who changes water. Start thinking like an aquaponics gardener who manages a balanced ecosystem. You add water to replace what is lost, and you rarely change it to remove waste, because your plants are doing that job for you.

 

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