WATER QUALITY

What You Need To Know

To Keep Your Fish Alive

Gary Fornshell, University of Idaho

Terry Patterson, College of Southern Idaho

To a great extent, the success or failure of

fish culture is determined by water

quality

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 Variables

• Hardness 50 – 100 mg/L as CaCO3

• pH 7 – 8

• Carbon dioxide < 20 mg/L

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%

Water Balance in Freshwater Fish

Salts

Large quantitiesof dilute urine

Ammonia

Water

Stressors

• Poor water quality

• Environmental conditions

• Improper handling

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

Resources• SRAC Publications: http://www.msstate.edu/dept/srac/publicat.htm

• Hach WQ test kits: http://www.hach.com/

• LaMotte WQ test kits: http://www.lamotte.com/

• Equipment Suppliers:

• http://aquaticeco.com/

• http://www.tecinfo.com/~aqcenter/

• Eagar, Inc. 1-800-423-6249