Quick facts
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Clean your water tank often throughout the year to prevent algae growth and unclean conditions.
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Always use bleach in the recommended amounts and follow the respective wait time.
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Don’t use scented bleach products.
Water is one of the seven key nutrients required by horses. Horses should always have access to good quality water. Frequent water tank cleaning is important, especially in warm months and with plastic tanks.
How to clean your water tank
Empty the tank.
Scrub it clean.
Rinse the tank with a 10 percent bleach solution (1 part bleach to 9 parts water).
Rinse it twice more with clean water.
Refill the tank. The horses can safely drink from it right away.
Adding bleach to your water tank
You can add small amounts of bleach to existing water in a tank at a level that is safe for your horse to drink.
- Effectively disinfect water in tanks by using unscented household bleach in recommended quantities.
- After adding bleach, wait at least one hour before letting your horses drink from it. This will allow the chlorine time to dissipate.
- If the water is less than 50 degrees F, increase the waiting period to two hours.
If you want to treat water from a lake, stream or shallow well, double the amount of bleach you use and wait two hours before letting your horse drink. These water sources can contain chlorine resistant parasites from animal droppings.
Always use the recommended bleach levels and wait the recommended amount of time to prevent over application, which can lead to toxicity. The table below outlines how much bleach to add to specific amounts of water to disinfect relatively clean water. Only use unscented bleach products.
| Gallons of water to disinfect | Amount of bleach needed* |
|---|---|
| 1 | 2 drops |
| 5 | 11 drops |
| 50 | 1 3/4 teaspoons |
| 100 | 3 1/2 teaspoons |
| 500 | 6 tablespoons |
*Will produce water with about 2 parts per million of chlorine.
How often should you clean your water tank?
You should clean your water tank often, even in the winter, to avoid algae growth and unclean conditions. Algae growth may cause your horse to drink less and can be toxic in some cases.
What affects water quality in your tank?
Many factors contribute to a dirty stock tank and poor water quality. Dirt, manure, feed droppings and algae can all contaminate tank water.
In small amounts, algae can turn the water green and produce a bad odor, which may reduce how much water your horse drinks. In larger amounts, algae can make your horse sick.
Water temperature can greatly affect horse water intake. Generally, horses prefer cool to lukewarm water over hot or very cold water.
Total dissolved solids (TDS) is the main measurement used to assess water quality for livestock. TDS values below 1,000 parts per million (ppm) are considered safe for all classes of horses.
Water turbidity, or the overall clarity of the water, is another way to assess water quality. Typically, water should have a turbidity value less than or equal to 5 NTUs (nephelometric turbidity units) for human drinking water.
There are no ranges or limits that exist for horses or other livestock. However, a fairly clear water source with a turbidity value of 25 NTU is considered acceptable for a horse.
Plastic or metal tank?
During a 2019 University of Minnesota study on whether adding goldfish to water tanks improves water quality, we found that using metal tanks may promote lower turbidity and algae than plastic tanks, meaning water quality may stay higher longer in metal than plastic. This could be due to rough plastic surfaces being harder to clean.
Water temperature affects water quality
There was no difference in water temperature between the plastic or metal tanks in the study. For every 1 degree increase in air temperature, water temperature increased by 0.60 degrees.
For every 1 degree increase in water temperatures:
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TDS increased by 0.80 mg/L.
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Turbidity increased by 0.65 units.
Our study, published in the Journal of Equine Veterinary Science, could not conclusively recommend using goldfish as a management method for maintaining water quality in water tanks.
Study highlights:
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Goldfish do not improve water quality but may reduce total dissolved solids.
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Metal tanks had lower turbidity and chlorophyll a than plastic tanks.
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Total dissolved solids and turbidity increased as water temperature increased.
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Frequent cleaning is important, especially in warm months and with plastic tanks.
Testing water quality control when using goldfish
We conducted an experiment to test the effects of two tank types (plastic and metal) and goldfish on water quality.
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There were four 100-gallon stock tanks, plastic and metal, both with and without goldfish.
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We used a stocking rate of 20 gallons per goldfish for a total of 5 goldfish per tank.
- Every day we recorded air temperature, water temperature, TDS, and water turbidity.
- We sampled water to determine algae once a week.
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After 28 days, we set aside the goldfish in holding buckets and scrubbed the tanks clean by hand and refilled them. We acclimated the goldfish to the temperature of the fresh water in their holding buckets and then released them into the water.
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We added water to all the stock tanks when any of the tanks were halfway gone. We used this value to determine if horses preferred one tank over another.
Did goldfish make a difference?
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TDS gradually increased throughout each 4-week period, and plastic tanks with fish had lower TDS compared to metal tanks without fish.
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Goldfish did not affect water turbidity. However, metal tanks had an overall lower turbidity value compared to plastic tanks.
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Goldfish did not affect algae content of the tanks. However, metal tanks had less algae compared to plastic tanks.
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There was no effect of tank type or goldfish on horse water intake. Horses drank out of all tanks equally.
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There was a high death rate among the goldfish in the study.
Average water quality parameters of plastic and metal water tanks with and without goldfish
| Tank type | Total dissolved solids (ppm) | Water turbidity (NTU)* | Chlorophyll a (mg/m3) |
|---|---|---|---|
| Plastic (with goldfish) | 233 | 18.4 | 13.2 |
| Plastic (without goldfish) | 235 | 18.4 | 13.2 |
| Metal (with goldfish) | 254 | 9.3 | 7.1 |
| Metal (without goldfish) | 259 | 9.3 | 7.1 |
*Adding goldfish to the tank had no effect on water turbidity or chlorophyll a (chlorophyll a indicates the presence of blue-green algae).
We conducted a survey of horse owners and managers available from October 31 to December 2018.
The survey consisted of five to nine questions regarding water tank and fish use, along with five demographic questions. The first survey question asked if a participant had previously used, currently used, or had never used goldfish or other aquatic species in tanks. Based on the response to the first question, participants were asked slightly different questions. However, all participants were asked the same demographic questions.
Survey results
We received a total of 672 completed surveys.
When asked about prior use of goldfish in water tanks:
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56 percent of respondents had never heard of nor used fish species in their horses’ water tanks.
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26 percent of respondents had used fish before.
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18 percent of respondents currently used fish.
Of respondents that used fish, 88 percent used common goldfish with a stocking rate of 1 to 6 fish per 100-gallon tanks. Of those who no longer use fish:
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22 percent stopped because they felt fish did not work or did not reduce time spent cleaning.
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43 percent stopped because the fish died.
When asked about cleaning water tanks:
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27 percent of horse owners and managers indicated they cleaned water tanks once per week.
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12 percent had never cleaned their horses’ tanks. Of individuals who had never cleaned their tank, 86 percent currently used, or had previously used, fish to maintain water quality.
Devan N. Catalano, Bradley J. Heins, Shahram Missaghi, Marcia R. Hathaway, Krishona L. Martinson, "The Effect of Goldfish (Carassius auratus) on Water Quality in Horse Stock Tanks," Journal of Equine Veterinary Science, Volume 79, 2019, Pages 73-78, ISSN 0737-0806, https://doi.org/10.1016/j.jevs.2019.05.016. (http://www.sciencedirect.com/science/article/pii/S0737080619303351)
Reviewed in 2023