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Unit 3.1 Water Quality Dynamics

2. WATER QUALITY DYNAMICS
AQUAPONICS
WATER QUALITY DYNAMICS
Unit 3.1 Water Quality Dynamics

3. Water Quality Dynamics
pH most important parameter
Affects other water quality parameters
Ammonia
Nitrite
Nitrate
Alkalinity
Electrical conductivity (EC)
Dissolved oxygen (DO)
Test kits and/or electronic meters
Needs/costs

4. pH
Power of hydrogen
Negative logarithm of the hydrogen ion (H-) concentration
pH change from 6.0 to 7.0 would be a tenfold decrease in hydrogen ion concentration
6.0 to 8.0 would be 100 fold decrease; times more acidic than 8.0
Measure of the amount of hydrogen ions in the water
Expresses intensity of acidic or basic characteristic of the water
< 7.0 acidic
>7.0 basic
7.0 neutral
Basic sometimes referred to as alkaline but alkalinity is the measure of the buffering capacity of water

6. ph Controlling factor for chemical balances
Ratio of nontoxic ammonium ion (NH4+) to toxic ammonia (NH3)
Ratio of toxic nitrite ion (NO2-) and very toxic nitrous acid (HNO2)
Ideal pH for aquaponics a compromise for
Fish
Plants
Bacteria
> 7.2 harder for plants to absorb nutrients
< 7.0 nitrification slows
Nitrification creates nitrous acid – naturally lowers pH

7. ph pH below 4 and above 11 is fatal to almost all fish species
Growth and reproduction are affected at levels of 4-6 and 9-10
Other factors that affect pH
Chemical reactions
Alkalinity
Hardness
Time of day (CO2 levels)
Respiration increases CO2 and lowers pH
Photosynthesis removes CO2 and raises the pH

8. Ph adjustment and nutrient supplementation
Monitor pH daily
Target range
If pH is lower that 7.0 alternately add calcium hydroxide[Ca(OH)2]/potassium hydroxide (KOH)
Always add to pH adjustment tank or add to water to be added to the system – never directly input into system
Supplements calcium and potassium into the system - both of which can be deficient
Do not add sodium bicarbonate (baking soda; NaHCO3) – raises the level of sodium in the system

9. Ph adjustment and nutrient supplementation
Iron (Fe) can also be deficient in aquaponics – add chelated iron Fe-DTPA – soluble at 7.0
2.0mg/L
If the pH is higher than 7.5 reduce by using nitric, phosphoric, or acetic acid in very small quantities until pH reaches the desired levels
Before addition of acids or bases to system determine rate of application
Remove given volume of water from system
Test the pH
Add acid or base in small amounts until desired pH is reached
Calculate the amount needed for the entire system volume
Add to pH adjustment tank
Don’t shock fish or plants with rapid pH fluctuations

10. Microbial Processes
>50% of waste produced by fish is in the form of ammonia
Gills, urine
Fecal matter – mineralization – heterotrophic bacteria consume fish waste, decaying plant matter, and uneaten food converting all to ammonia and other compounds
Sufficient quantities of ammonia are toxic to plants and fish
Nitrifying bacteria convert ammonia to nitrite and then to nitrate – plants consume the nitrate
Bacteria attach to
Tank walls
Underside of rafts
Organic matter
Growing medium
Water column

11. Microbial Processes
pH <7.0 slows nitrification process and 5.0 or lower ceases nitrification
Ammonia and nitrite quickly rise to toxic levels

12. Ammonia 2 forms (total ammonia) <3.0mg/L
Toxic unionized ammonia (NH3) - <0.01mg/L
Less toxic ionized ammonium ion (NH4+)
Amount of each form present is dependent on pH
Temperature
As these increase toxic form increases

13. Nitrite and nitrate Nitrite (NO2) Ammonia – Nitrosomonas – Nitrite
Toxic to fish; interferes with fish’s ability to use oxygen
>1.0mg/L unsafe for most fish
pH dependent
Nitrate (NO3-)
Nitrite – Nitrobacter - Nitrate
Relatively nontoxic to fish
Primary source of nutrition for the plants

15. Water temperature Temperature affects many biological processes
Feeding
Reproduction
Metabolism
Amount of oxygen (cool water has more oxygen than warm water)
Tilapia – warm water fish - 70°-74°F
Compromise between plants and fish
>75°F too warm for roots and plants will not grow as robust
More susceptible to fungus and pathogens such as pythium

16. Dissolved oxygen (do)
Optimal levels for aquaponics 80% saturation (6-7mg/L)
<3mg/L stress aquatic life
<1mg/L lethal
Low levels result from
Cloudy weather
Rain
Heavy stocking
Feeding rates
Low levels indicated by
Loss of appetite by fish
Piping
Grouping around inflow pipe
Slowed growth
High incidences of disease and parasites

17. Dissolved oxygen (do) Affected by Temperature Salinity
Warm water less DO than cool water
Saline water less do than fresh water
Important water quality parameter and should be checked regularly
Meters range from $100’s to $1000’s
Test kits less costly but not as quick or accurate

18. alkalinity
Measure of pH buffering capacity – acid neutralizing capacity of water
Expressed as calcium carbonate (CaCO3) mg/L
Measured by titration with sulfuric or hydrochloric acid
50 to 300mg/L acceptable for aquaponics

19. Reference
Nelson, R. L. Aquaponic Food Production Raising Fish and Plants for Food and Profit Nelson and Pade, Inc. Montello, WI. Pgs
With contributions from John S. Pade