5. Water From the perspective of food safety, the source of water used in aquaponic systems has the potential to have a significant bearing on the quality of the final products, whether they are fish or plants. In Alberta, deep wells or municipal supplies of water are the most common sources of water for experimental or commercial aquaponic systems, all of which are currently indoor facilities. According to Hutchings (2003), at least two of the deep-well sources of water for privately owned aquaponic systems in the province have a high totalsalt content and generally, are not suitable for the growth of plants or freshwater fish. In terms of water quality, and the concentrations of salts and minerals needed for the production of sweet basil (or general guidelines), Racozy (2003b) noted: ‘Our general guideline is to feed fish at a ratio of 57 grams per m2 of plant
growing area per day. This ratio provides good nutrient levels. We supplement with equal amounts calcium hydroxide and potassium hydroxide to maintain pH near 7.0. Every three weeks we add 2 mg/L of iron in the form of a chelated compound. In a commercial-scale aquaponic system at UVI (University of the Virgin Islands) that was to produce lettuce continuously for 2.5 years, nutrient concentrations varied within the following ranges (mg/L) that would have produced excellent sweet basil growth’:
Calcium - 10.7-82.1
Phosphate P - 0.4-15.3
Copper - 0.01- 0.11
Magnesium - 0.7-12.9
Sulfate S - 0.1-23.0
Zinc - 0.11-0.80
Potassium - 0.3-192.1
Iron - 0.13-4.3
Boron - 0.01-0.23
Nitrate N - 0.4-82.2
Manganese - 0.01-0.19
Molybdenum - 0.00-0.17
13