Understanding and Maintaining Water Quality
 The variables to be measured
 Temperature
 Dissolved Oxygen
 pH
 Nitrite and Nitrate
 Salinity
 Alkalinity and Hardness
 Ammonia
 Plant nutrients
 Fertilization
 Controlling undesirable plants
 Light, substrate, suspended solids
 Water effects on cultured organisms
Parameter
Value
Dissolved oxygen
mg/L O2
Water temperature
C (Celsius)
pH
Total ammonia nitrogen
mg/L N
Nitrite
mg/L NO2-
Nitrate
mg/L NO3-
Alkalinity/Hardness
mg/L CaCO3
Salinity
g/L salt
 Temperature
- Vary in water bodies
- Vary in water sources
- Very important in maintaining fish or other
organism’s activity
- Measured by various kinds of thermometers
- Various ways in farm design
 Dissolved Oxygen
- All cultured organisms are aerobic, i.e., they respire
oxygen
- Oxygen level in the various kind of water bodies
vary
- Oxygen level in various layers of the water body
vary
- Measured using various instruments, kits or
chemical methods
- Various ways to maintain it
- dissolved oxygen and water temperature usually vary
over a 24 hour cycle
Stratification can cause dissolved oxygen and
temperature to vary at different depths in the same
system.
 pH
- One of the very important factors
- Hydrogen ion concentration
- A near neutral pH is usually good for most of the
organisms
- Some species requires narrow range while other
tolerate a wider range
- Measured by portable or lab-scale pH meters,
sometimes by strips
- Maintained by various ways
 Ammonia
-Total ammonia nitrogen is a measure of the ammonia
(NH3) and ammonium levels (NH4+) in the water
- The ratio of ammonia and ammonium varies in an
equilibrium determined by pH and water temperature.
90 %
80 %
NH3 as % of TAN
70 %
at 20 C
at3 0C
60 %
50 %
40 %
30 %
20 %
10 %
9.8
9.4
9
8.6
8.2
7.8
7.4
7
0%
pH of water
Ammonia as a % of total ammonia nitrogen
 Nitrite and Nitrate
- Nitrites and nitrates are produced by an aerobic
bacterial nitrification process of ammonia by
Nitrosomonas and Nitrobacter respectively.
- Nitrites are toxic to aquatic organisms, usually by
being actively transported across the gills to bind
with hemoglobin (making methemoglobin) which is
incapable of transporting oxygen.
- Nitrates are usually not toxic unless in very high
concentrations.
 Alkalinity and Hardness
- The form alkalinity takes is linked to pH of the
system.
- Alkalinity buffers against diurnal variations in
pH.
 Salinity
- Freshwater has a low ionic concentration (i.e.
streams, rivers, ponds and lakes).
- Saltwater has a high ionic concentration (ocean
waters).
- Brackishwater has an ionic concentration between
freshwater and saltwater (mangroves).
- NaCl concentration
- Freshwater is less than 2 g/L
- Brackish water is 2 g/L to 34 g/L
- Sea water is more than 34 g/L
 Plant nutrients
 Fertilization
 Controlling undesirable plants
 Light, substrate, suspended solids
 Water effects on cultured organisms