Abstract

Explosive growth in the private ownership of koi has brought a corresponding increase in equipment and water treatments sold to reduce turbidity in koi ponds. Although claims by manufacturers and retailers offer results in descriptive terms, there currently are no standards to scientifically compare these claims. Additionally, a standard protocol for measuring turbidity, both quantitatively and qualitatively, should be established to address water quality problems. A proposed protocol has been developed and used effectively to measure turbidity in koi ponds.

Methodology

A representative sample is taken and immediately analyzed for turbidity using a colorimeter.ⁱ The results, in formazine attenuation units (FAU), are noted as T0. The sample is allowed to remain undisturbed for 10 minutes and then retested. The results noted as T10. The settled sample is then centrifuged at low speed (2300 RPM) for 6 minutes (urinalysis setting).ⁱⁱ The supernatant is then retested for turbidity and the results noted as Ts. The residue after centrifugation is pipetted onto a glass slide and analyzed qualitatively, first unstained, then after addition of a urine sediment stain.ⁱⁱⁱ The supernatant is then treated with a water clarifier^iv and allowed to stand for 24 hrs. The sample is then centrifuged and the supernatant retested and noted as Tc. This result represents water color.

Discussion

There are at least 4 reasons to establish a testing protocol for turbidity.

1) Increased turbidity may represent evidence of a water quality problem in a koi pond. Analysis may help solve health problems. 2) The koi practitioner may also be contacted to solve turbidity problems when no health problems exist, as modern equipment has enabled pond keepers to achieve very high water clarity and enthusiasts expect this. 3) Even when treatment results in improvement in pond clarity, these changes may take several weeks to be truly evident and a method to quantify small improvements may be desirable to satisfy the pond keeper. 4) Comparability between systems may be evidenced in only very subtle differences. Equipment and water treatment manufacturers and retailers often laud their products as helping to achieve high clarity water, using descriptive terms (such as "gin clear water"), but which are not standardized for comparative purposes.

Standardized turbidity measurement is based on distilled water reading 0 FAU. All tap water tested to date has tested at 0-1 FAU. Margin of error on all tests is ± 1 FAU.

T0 represents the total turbidity of the pond water, as it exists in the pond, and before correction for water color. In excellent koi pond systems, the usual range is 1-2 FAU. Water giving this reading requires no further analysis.

T10 represents the pond water minus settleable solids. Any difference between T0 and T10 should be investigated, as the presence of settleable solids in the water column is undesirable. Some examples causing this condition are the use of air diffusers in the pond, excessive turbulence from multiple waterfalls, and air leaks into bead filters.

Ts represents the pond water after removal of suspended solids, planktonic algae, and other organisms down to a size of about 1 micron. Coupled with microscopic examination of the resultant sediment, it is very useful in addressing problems of a subtle planktonic algae bloom (lack of or failure of UV clarifier), emulsification of feces (pumping of bottom waste), or foreign matter in pond water (pollen).

If Ts is still greater than 1-2 FAU, the sample is treated with a water clarifier (1 drop/ 250cc) to remove bacteria and other suspended organic and inorganic substances. The sample is allowed to stand for 24 hours and centrifugation is repeated. The supernatant is retested. The reading Tc represents the color of the water after the removal of all suspended solids. This value is subtracted from T0, T10 and Ts to give the true turbidity readings. Elevated true Ts readings have been seen with high bacterial loads (dead fish in pond), high levels of dissolved organics (inadequate circulation or oxygenation of water, poor or no filtration).

Water color (staining) can be high (greater than 6 FAU). In some cases, it may represent the only problem (T0=T10=Ts= Tc). With koi pond depths now often 1-3 meters, even staining of a few FAU can be evident on the white color of many varieties of koi (Platinum Ogon, Kohaku, Shiro Bekko) at these depths.

The source water for the pond can be evaluated as above to determine if problems are intrinsic to the pond or imported with the source water. This will help evaluate the benefits of frequent or massive water changes in correcting the problem.

Endnotes

i. DR/890 colorimeter--Hach Co.,PO Box 608, Loveland, CO 80539-0608
ii. Triac centrifuge--Clay Adams, Div. of Becton Dickinson and Co., Franklin lakes, NJ, 07417
iii. Urinary sediment stain VUS-030--Volu-Sol, Inc.,5095 West 2100 South, Salt Lake City, Utah 84120
iv. It's Clear--Florida Aqua farms, Inc., 33418 Old Saint Joe Rd., Dade City FL 33525