1. WATER QUALITY
What You Need To Know
To Keep Your Fish Alive

2. To a great extent, the success or failure of fish culture is determined by water quality

3. Water Quality – Why Is It Important?
Your fish live in it
Are supported by it
Receive their oxygen from it
And excrete in it 3

4. 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

5. 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

6. Water Quality Variables
Temperature
Dissolved oxygen
Total ammonia-nitrogen, NH3, NO-2
Alkalinity
Hardness pH
Carbon dioxide

7. Water Quality Variables Temperature
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 °F

8. 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

9. 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) ,

10. Percent of Total Ammonia in the Un-Ionized Form at Various Temperatures and pH
percent Ammonia
Temperature (ºF) (pH)
___________________________________________
50º
68º
86º

11. The Nitrogen Cycle Food Water plants Excess food Fishes Algae Feces
Peptides
Amino acids
Urine
Urea
Ammonia
(NH )
Algae
Nitrate (NO )
Nitrite (NO )
Feces 2 3

12. for Bio-Filter to Mature
Time Required
for Bio-Filter to Mature
0.8 8 NO 3
0.6 NO 6 2 NH 3
Nitrites &
Nitrates
(mg/l)
Ammonia
(mg/l)
0.4 4
0.2 2
0.0 2 6 10 14 18 22
Time in Days 22

13. Water Quality Variables - Alkalinity
Is the buffering capacity of water –
absorbs acids and/or bases
High alkalinity prevents wide pH fluctuations
Maintain levels between mg/L as CaCO3
7 grams of alkalinity consumed by 1 gram of NH3

14. Effects of pH on Various Buffers
Percent of Total CO 2
100 - =
Free CO
HCO CO 2 3 3 50 4 5 6 7 8 9 10 11 12 pH

15. Water Quality Variables
Hardness – 100 mg/L as CaCO3
pH – 8
Carbon dioxide < 20 mg/L

16. Water Quality Variables
Total 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%

17. Water Balance in Freshwater Fish
Salts
Ammonia
Large quantities
of dilute urine

18. Stressors Poor water quality Environmental conditions
Improper handling

19. 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.

20. Low Level Mortality
100%
Peracute M O R T A L I Y
Acute
Usually the first sign of water quality/environmental problems
Chronic 0%
Time

21. 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

22. 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

23. 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

24. Good Stuff To Know
~ 300 square feet biofilter material per 100 lbs. fish
Add to lbs. baking soda/ 100 gallons to maintain alkalinity
Add to 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

25. Resources
SRAC Publications:
Hach WQ test kits:
LaMotte WQ test kits:
Equipment Suppliers:
Eagar, Inc