JUNE 20, 2025
Better RAS Water Quality: How Algae Cultivation Supports Filtration and Farm Performance
Stan Pankratz
Founder / President
Recirculating Aquaculture Systems (RAS) are built to make fish farming cleaner and more efficient. But maintaining stable water quality remains a key challenge, especially as farms scale up and fish density increases.
A practical solution gaining traction is microalgae cultivation used alongside standard biofiltration. This is not about replacing what works but improving how the system handles what remains.
At the Aquaculture Canada Conference and Tradeshow 2025 in Fredericton, Rainforest Algae shared how algae biofiltration has the potential to provide a natural, cost-effective layer of control to address the core water quality issues many RAS farms face.
Dr. Stan Pankratz speaking at Aquaculture Canada Conference 2025
The Core Water Quality Hurdles
In any RAS setup, nitrifying bacteria convert ammonia into nitrate. This protects fish from toxic ammonia, but nitrate builds up over time. Meanwhile, fish and bacteria generate CO₂, affecting dissolved oxygen balance, lowering pH, resulting in increased fish stress, and reducing biofiltration effectiveness. To overcome the high nitrate concentrations and low dissolved O2, more frequent water exchanges are required.
Closed tank environments can also become breeding grounds for unwanted bacteria. Over time, this raises disease risk and increases the need for treatments.
How Algae Provide Extra Support
When grown purposefully, microalgae naturally help stabilize the system by:
- Absorbing nitrate before it accumulates
- Using CO₂ as a nutrient while releasing oxygen through photosynthesis
- Supporting a healthier microbial balance, which helps reduce disease risk
- Creating biomass rich in protein and omega fatty acids that can be processed into feed ingredients
The result is cleaner water, less chemical input, and fewer water exchanges.
Proven Species for Hatcheries and Grow-Out
Algae supplements that could be cultivated onsite to provide nutritional benefits for the fish improving water quality include:
| Species | Nutritional Features | Common Use |
|---|---|---|
|
Isochrysis galbana (T-ISO) |
High DHA, amino acids, sterols |
Larval bivalves, some crustaceans |
|
Chaetoceros muelleri |
High EPA, supports shell formation |
Bivalve spat, scallops |
|
Tetraselmis suecica |
Lipids, vitamins, antioxidants |
Finfish larvae, rotifers |
|
Nannochloropsis oculata |
High EPA, robust culture |
Rotifer enrichment, larval fish |
|
Thalassiosira pseudonana |
Silica-rich diatom, protein |
Bivalves, crustaceans |
Cultivating these on-site keeps costs lower than relying on imported paste or pellets.
Economic Feasibility and Pilot Data
In practice, a compact algae culture unit can run outdoors using sunlight with supplemental lighting during colder seasons. Algae paste yields may reach 0.8-1 kg/d depending on species and operating factors and requiring ~100 kW energy / day (~$20-25/day) which translates into $2.50/ kg wet paste. Compare these costs with commercial nutrient products.
Algae cultivation units could potential replace CO₂ degassing stage, because of effectiveness to remove dissolved CO2 and to boost oxygen naturally.
Pilot Projects
Rainforest Algae is looking to work with aquaculture partners and researchers to validate algae cultivation under real-time operating conditions. Trials track nitrate levels, pH and oxygen stability, fish health, and cost efficiency.
The goal is to demonstrate that algae cultivation offers a practical solution that also impacts economic aquaculture performance.
Key Takeaways for RAS Operators
Adding algae cultivation works with existing filtration to close the nutrient loop and protect fish health. Benefits include:
- Lower nitrate levels
- Balanced CO₂ and steady oxygen
- Less chemical treatment
- Feed savings from homegrown biomass and feed conversion ratios
Stronger sustainability for buyers and certification
Talk with Us
Rainforest Algae helps farms plan, test, and expand algae cultivation suited to their specific water conditions and production goals. This is an investment worth exploring for operators wanting stronger water quality control and more value from every unit of feed.
Contact us to learn more or join an active pilot project.
📧 info@rainforestalgae.ca
📧 stan.pankratz@rainforestalgae.ca
🌐 rainforestalgae.ca
📞 403 616 0555
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