Are your plants in the sun? Plants grow by photosynthesis, which requires light of at least 30,000 Lux. We use a light meter on farms where plants are not in direct sunlight, and don’t bother with light determinations where plants are in the sun.
Are your fish tanks shaded? If not, algae can grow and use up the nutrients.
Are your fish feeding to satiety? We normally ask the farmer how much food the fish eat, and then conduct our 10 min satiety test. In all cases we have found that the fish were being underfed. This leads to fertilizer nitrate levels that are too low.
What is your nitrate nitrogen level? When these are low (<15 mg/L) there is probably some denitrification occurring; when this occurs, we use the DO meter to find low DO spots, which must be corrected.
Have you considered switching to a trickle gravel system? Our research has found these are more efficient systems that are easier to maintain.
How is your organic certification going? Organically certified vegetables sell for between $3 and $4 per pound. Prices are the largest determinant of profitability according to Tokunaga et al (2014).
Are your fish dying? If so, unionized ammonia or nitrite may be too high in the system, and biofiltration needs to be boosted.