WATER QUALITY
What You Need To Know
To Keep Your Fish Alive
Gary Fornshell, University of Idaho
Terry Patterson, College of Southern Idaho
Water Quality – Why Is It Important?
• Your fish live in it• Are supported by it
• Receive their oxygen from it• And excrete in it
Water Quality – Why Is It Important?
• Water quality factors influence and interact with each other
• What may cause problems in one situation may be harmless in another
• Influences effectiveness/toxicity of treatments
Water Quality – Why Is It Important?
• Most disease problems can be avoided with proper management of water quality
• This includes maintaining water quality at a level that provides an environment
conducive to fish health and growth
Water Quality Variables
• Temperature
• Dissolved oxygen
• Total ammonia-nitrogen, NH3, NO-2
• Alkalinity
• Hardness
• pH
• Carbon dioxide
• For each 10°C (18°F) rise in
temperature the metabolic rate doubles
• Controls the reaction rate of chemicals
• Influences solubility of gases in water
• Influences toxicity of ammonia and therapeutants
• Optimum temperature for tilapia growth is 85-88 °F
Water Quality Variables Temperature
Water Quality Variables Dissolved Oxygen
• First limiting factor for growth and fish health
• Solubility decreases with increasing temperature and elevation
• Respiratory rate increases with increasing temperature, activity and feeding
• In general the minimum DO should be ≥ 60% of saturation or ≥ 5 ppm (mg/L)
• > 2 ppm in biofilter effluent
Water Quality Variables
Total Ammonia-Nitrogen
• Usually the second limiting factor – nitrogenous waste: feces & feed
•TAN includes ammonium ion (NH4+)
and ammonia (NH3)
• The proportion of NH3 increases with increasing temperature and pH
• < 0.05 mg/L NH3
• < 0.5 mg/L nitrite-N (NO-2) ,
Percent of Total Ammoniain the Un-Ionized Form at
Various Temperatures and pH
percent Ammonia
Temperature (ºF) (pH) 7.0 8.0 9.0___________________________________________
50º 0.19 1.83 15.768º 0.40 3.82 28.486º 0.80 7.46 44.6
Water plants Food
Excessfood
Fishes
PeptidesAmino acids
Urine
Urea
Ammonia(NH )
Algae
Nitrate (NO )
Nitrite (NO )
Feces
2
3
3
The Nitrogen Cycle
0.8
0.6
0.4
0.2
0.02 6 10 14 18 22
8
6
4
2
0
Ammonia(mg/l)
Nitrites &Nitrates(mg/l)
NHNO
NO
23
3
Time in Days
Time Requiredfor Bio-Filter to Mature
Water Quality Variables - Alkalinity
• Is the buffering capacity of water –
absorbs acids and/or bases
• High alkalinity prevents wide pH fluctuations
• Maintain levels between 75-120 mg/L as CaCO3
• 7 grams of alkalinity consumed by 1 gram of NH3
100
50
04 5 6 7 8 9 10 11 12
Free CO HCO CO
Percent of Total CO 2
3- =
2 3
pH
Effects of pH on Various Buffers
Water Quality VariablesTotal Dissolved Gases
Supersaturation caused by:
• leaking water lines
• air leak on low pressure side of pump
• source of water
• mixing cold and hot water
Recommended total dissolved gas pressure <104%
Most Fish Diseases Are Stressed Mediated
Stress is a physiologic state caused by a procedure, environmental condition or other factor which interferes with the fish’s ability to maintain a “normal” state. It extends the adaptive responses of an animal beyond the normal range or which disturbs the normal functioning.
Low Level Mortality
100%
M
O
R
T
A
L
I
T
Y
0%
Peracute
Acute
Chronic
Time
Usually the first sign of water quality/environmental problems
Loading Effects
Number of fish which can successfully live and grow in a given amount of water depends on:
• DO level
• Metabolic rate of the fish
• Amount being fed
• Pathogen load
• Water exchange rate
Management Recommendations
• Maintain water quality within suggested guidelines
• Maintain fish loadings at optimum levels of 1/4 to 1/3 lb./gallon (1/2 lb./gallon maximum)
• Monitor water quality on a regular basis/keep good records
Management Recommendations
• Low DO: increase aeration; stop feeding
• High CO2: increase aeration; add air stripping column
• Low pH: add sodium bicarbonate; reduce feeding rate; check ammonia & nitrite
• High NH3: exchange system water; reduce feeding rate; check biofilter, pH, alkalinity & DO in biofilter
• High nitrite: exchange water; reduce feed; add 6 ppm chloride per 1 ppm nitrite; check biofilter, pH, alkalinity & DO in biofilter
Good Stuff To Know• ~ 300 square feet biofilter material per 100 lbs. fish
• Add 0.125 to 0.167 lbs. baking soda/ 100 gallons to maintain alkalinity
• Add 0.275 to 0.413 lbs salt/100 gallons to maintain chloride levels of 200 – 300 ppm
• Do not make any rapid changes to any WQ parameter, except to increase DO