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Statistical evaluation of ammonia levels in show vats at koi shows

(Validation for the choice of 0.5 mg/L as an achievable, safe total ammonia level in unfiltered vats)

General:
 
Research has shown that long term exposure to free ammonia (NH₃) levels below 0.02 mg/L do not cause harm to fish.  In c1992, OATA produced a table of ammonia values for a wide range of pH and temperatures. If the total ammonia level (most test kits only measure total ammonia) is maintained below the level indicated on the table for the appropriate pH and temperature, then the free ammonia level will not exceed the safe level of 0.02 mg/L. This table should be adhered to in koi ponds and in all other biologically filtered systems where the exposure of fish to that level of ammonia is continuous.  The OATA table was designed to cover the varied situations existing in ponds and aquaria of all kinds.  A similar table has been calculated to cover the range of pH and temperatures appropriate to koi keeping, and as a result, this new expanded koi-specific table gives more detail in this range.  Both tables were calculated from original source data published by Liao (1972), which was refined by Spotte (1979)  and further refined into a four figure accurate data set by Kordon (date unknown, circa mid 1980s).  Both the OATA and the new koi-specific table were calculated by slightly different mathematical methods and show close correlations in the areas where they intersect, therefore both tables mutually validate each other and are suitable to be used as a standard in biologically filtered systems.

Koi will tolerate short term exposure to higher levels of ammonia without harm.  Values from the OATA table or from the koi-specific table are unachievable at koi shows when the local pH and water temperatures are high. In these situations, a more realistic value of total ammonia is desirable.

Data sources:

Fish welfare. By Edward J. Branson:  MRCVS, Veterinary Surgeon, RCVS Specialist in Fish Health and Production. Monmouthshire, UK.
States that: “Thurston et al (1981) reported that test fish tolerated constant concentrations of ammonia better than fluctuating levels”.
(It is therefore better for koi welfare at koi shows to adopt a sensible and achievable level, albeit a little higher than values obtained from ammonia charts, rather than conduct excessive and repeated water changes in an attempt to achieve unrealistically low values).

Effect of dietary protein level on excretion of ammonia in Indian major carp.  By Chakraborty & Chakraborty:  Department of Fisheries Technology, Bangladesh Agricultural University, Bangladesh 1998.
Rupert Bridges quoting Chakraborty states:
“at 20°C unfed common carp produce around 87 mg NH₃ per kg bodyweight per day”.
(An unfed Asian carp is the nearest analogy to koi carp under show conditions).

Koi body weight from weight calculators:
http://www.clearpond.com.au/go/help-centre/online-calculators/koi-weight-based-on-length-calculator
http://www.cnykoi.com/calculators/calclenw.asp

Manual confirmation of body weight (good fit):
http://www.coloradokoi.com/koi_weight.htm

Typical koi show example at a venue where pH is 8.5 and temperatures are 22°C to 25°C:
2.8 m vat stocked with 4 average size 6 + 4 average size 2 and with water testing every four hours

Average size 6 weighs 5.754 kg
Average size 2 weighs 0.453 kg

4 x average size 6’s:  23.016 kg
4 x average size 2’s:  1.812 kg
Total body weight in vat:  24.828 kg

A 2.8 metre vat contains 2464 litres of water at show depth.

Unfed carp excrete 87 mg ammonia per kg body weight per day.
That is 3.625 mg ammonia every hour per kilo body weight.

24.828 kg of unfed carp excrete 90.0015 mg ammonia per hour
90.0015 mg in 2464 litres of water raises ammonia level by 0.0365 mg/L
(Therefore: 4 average size 6’s + 4 average size 2’s raise ammonia in vat by 0.0365 mg/L per hour).

This ignores:

• Initial dumping after release from the travel bag.
• Ammonia from food or from koi feeding on algae and aquatic insects etc. prior to show.
• Stress.

If the showground pH is 8.5, and temperatures range from 22°C to 25°C then the maximum allowed total ammonia from the OATA table, (or koi-specific table), is between 0.16 mg/L and 0.13 mg/L.
(Aveley pH is 8.5, Newark up to 8.7, Aveley has reached 25°C, Newark has reached 22°C).

Table of total ammonia values in 2.8 metre show vat with 4 hour test regime in relation to target maximum levels for:-
Aveley showground; 8.5 pH and 25°C - value from OATA table = 0.13 mg/L
Newark showground; 8.5 pH and 22°C - value from OATA table = 0.16 mg/L
Safe, achievable alternative; 0.5 mg/L

Time Action Ammonia mg/L before water test Water change Ammonia mg/L after changes Target 0.13 mg/L Target 0.16 mg/L Target 0.5 mg/L Fri 13.00 Koi benched 0 No         Fri 15.00 Water test 0.0730 No 0.0730 OK OK OK Fri 18.00 Close vat (0.0730+0.1095) 0.1825 50%+50% 0.0456 Breached  by 40% Breached by 14% OK Sat 07.00 Open vat Water test (0.0456+0.4745) 0.5201 50%+50%+50% 0.0650 Breached by 300% Breached by 225% Slightly Breached Sat 11.00 Water test (0.0650+0.1460) 0.2110 50%+50% 0.0528 Breached by 62% Breached by 32% OK Sat 15.00 Water test (0.0528+0.1460) 0.1988 50%+50% 0.0497 Breached by 53% Breached by 24% OK Sat 18.00 Close vat (0.0497+0.1095) 0.1592 50%+50% 0.0398 Breached by 22% OK OK Sun 07.00 Open vat Water test (0.0398+0.4745) 0.5143 50%+50%+50% 0.0643 Breached by 296% Breached by 221% Slightly Breached Sun 11.00 Water test (0.0643+0.1460) 0.2103 50% 0.1052 Breached by 62% Breached by 31% OK Sun 15.00 Debenching (0.1052+0.1460) 0.2512 Not usual 0.2512 Breached by 93% Breached by 57% OK

Conclusion:

The table supports choosing to apply 0.5 mg/L total ammonia in preference to values from the OATA or koi-specific tables at venues where the showground water pH is high.  The value 0.5 mg/L total ammonia level in unfiltered vats is an achievable level under koi show conditions, even with a four-hourly water testing and changing regime.  In the typical vat scenario above, and calculating and measuring the total ammonia level in the vat to four decimal places, the two minor breaches of this level would have been barely measurable, even with modern electronic equipment. These minor breaches only occurred during the 13 hour overnight period when water testing and changing is not done, and mathematically, it can be shown that these minor breaches only existed for approximately the last 30 minutes of this 13 hour period before the early morning water changes would have reduced them.

Notes

Use of average weights for fish instead of maximum weight: The probability of every fish in a particular vat being at its maximum size for its particular size classification is very low, therefore it is valid to take the average size for each size classification and use this to be representative of the total body weight of fish in that vat.

Table is calculated to four decimal place accuracy:  When dealing with two decimal place numbers such as on the ammonia tables, it is usual to calculate to two extra digits to ensure that “rounding” errors are limited to less than 1%.

Water changes: To attempt to achieve the OATA (or koi-specific table) value of 0.13 or 0.16, very generous water changes have been used in the above table.  A total of 15 x 50% water changes still did not stop 0.13 being breached at every test after the initial test. Nor did it prevent 0.16 being breached in seven out of nine water tests.

Below is a suitable table of achievable total ammonia levels as calculated from Spotte (1979) / Kordon (date unknown) data sets and taking into account the validation of the above scenario.