M. R. McMurtry, D. C. Sanders, J. D. Cure & R. G. Hodson
This paper documents a year-long greenhouse experiment designed to answer a simple question: can iAVs remove nutrients from water and maintain stable water quality without constant chemical correction?
The study answers that question clearly and rigorously.
The researchers tested four different biofilter-to-fish-tank volume ratios across three sequential experiments. By changing only this single variable while holding all others constant, the study isolates cause and effect in a way that follows the scientific method cleanly: a defined hypothesis, controlled treatments, replication, measured outcomes, and statistical analysis.
No. Hydroponics depends on keeping nutrients dissolved in water at target concentrations. This system was designed to do the opposite. No fertilizer was added at any point. Fish feed was the only nutrient input. If nutrients accumulated in the water, that would have meant the system was failing.
Success here meant lower nutrient concentrations over time—not higher. The fact that it contains fewer nutrients, not more, is exactly what confirms that the iAVs system is functioning as intended. The cleaner the water, the better the system is performing.
Table 4 is the key piece of evidence for that last point. It shows the actual chemical analysis of the irrigation water at the end of Experiment 3, after a year of continuous operation. This is not theoretical, inferred, or modelled data. It is laboratory-measured concentrations of nutrients remaining in the water after biological filtration by sand, microbes, and plants.
No. The plants were not missing nutrients. Table 4 shows that dissolved nutrient concentrations in the irrigation water were low and declined further as biofilter size increased because the plants and microbial community were removing them efficiently. Despite lower water concentrations of elements such as phosphorus, magnesium, iron, and zinc, the crops showed no deficiency or toxicity symptoms.
This confirms that nutrients were present, supplied continuously via fish feed and mineralization, and taken up rapidly at the root zone—so low water concentrations reflect effective uptake, not nutrient shortage.
They were mineralized, taken up by roots and microbes, and converted into plant biomass, which is why concentrations stayed low in the water instead of accumulating in the water.
This study was done to see if iAVs can remove nutrients from water, a different study was done to see whether nutrients from fish waste actually ended up inside the tomato plants, and how changing the amount of fish waste affected that nutrient uptake, that paper is titled ‘Mineral nutrient concentration and uptake by tomato irrigated with recirculating aquaculture water as influenced by quantity of fish waste products supplied“.
Yes, pH was stable, but only when plants were present in the system.
pH stabilized at an average of 6.2 for the length of the experiment.
Yes — but only if the fish feed matches the nutrient profile used in the research. In the NCSU iAVs study, the plants were grown with no added fertiliser; all nutrients came from fish feed, and the paper explicitly reports the feed’s elemental composition (Table 4). The system worked because that feed supplied sufficient macro- and micronutrients without causing toxic accumulation.
If your fish feed does not closely match that composition, you should not expect the same results. Too little of a nutrient means deficiency; too much means toxicity. The system cannot create nutrients that are not present in the feed.
For commercial operators, the implication is simple: get your fish feed analysed, and if you’re operating at scale, use bulk purchasing to commission a custom feed formulation aligned with the iAVs nutrient balance. Without that, any claim that “fish feed alone is inadequate” is meaningless — it’s the wrong feed that’s inadequate, not the system.
Trained in environmental design and systems engineering, he designed, built, and operated the experimental systems and carried the project from conception through multi-year validation. His contribution was the core idea, the physical system, and the long-term empirical proof that sand could function simultaneously as biofilter, solids processor, and plant substrate. https://www.researchgate.net/profile/Mark-Mcmurtry
Douglas C. Sanders was a senior Professor of Horticultural Science at North Carolina State University and an internationally recognised authority on vegetable crop production. As McMurtry’s doctoral advisor, he ensured that plant growth, yield metrics, and nutrient interpretations met rigorous agronomic standards. His involvement anchored the work within mainstream horticultural science rather than experimental hobbyism. https://www.researchgate.net/scientific-contributions/DC-Sanders-2013466087
Ronald G. Hodson was Professor of Zoology and Director of the North Carolina Sea Grant College Program. A leading figure in applied aquaculture and fisheries science, he provided oversight of fish health, water quality thresholds, and production realism. His participation certified that the system met professional aquaculture standards and was suitable for serious food production, not just experimental demonstration. https://www.researchgate.net/profile/Ronald-Hodson
Jan D. Cure was a plant physiologist whose expertise bridged system-level performance and plant-level responses. Her contribution focused on physiological interpretation of nutrient uptake, stress tolerance, and growth under reciprocating irrigation conditions. She ensured that claims about plant health and nutrient sufficiency were grounded in plant biology rather than visual assessment alone. https://www.researchgate.net/scientific-contributions/Jennifer-D-Cure-2083191576
Yes, you can click this link to download a pdf copy of ‘Effects of Biofilter/Culture Tank Volume Ratios on Productivity of a Recirculating Fish/Vegetable Co-Culture System‘.
Never take anyone’s word as truth.
Critical thinking means pausing before you agree, asking what evidence supports a claim, who benefits from it, and whether alternative explanations exist. Check original sources, look for primary data rather than summaries, compare multiple independent references, and be wary of authority, popularity, or confidence being mistaken for accuracy.
If something matters, verify it yourself—truth holds up to scrutiny, and good ideas get stronger when they’re questioned.
“Believe nothing, no matter where you read it or who said it, unless it agrees with your own reason and your own common sense.” — Buddha
Original paper is also available at the publishers website, Taylor & Francis, at https://doi.org/10.1300/J028v07n04_03.