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Here you will find basic information on koi ponds as well as topics targeted towards ponds in a southern Canadian climate. Swimming Jewels is located in the sunny Okanagan Valley in a zone 4 growing region.


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The Nitrogen Cycle


Bacteria + Oxygen + Alkalinity = Clean Healthy Pond

sm. nitrogen cycle diagram.png
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 Parts of the Nitrogen Cycle


Ammonia - produced from the breakdown organic material in decaying; food, feces, dead plant & animal matter. Also excreted as waste by fish.

  • high levels of ammonia in water irritate gill tissue causing hyperplasia which reduces oxygen absorption and waste excretion ability

  • 1g of ammonia requires 4g of Oxygen to become nitrate

  • utilizes 7.1 mg of Kh(alkalinity) to remove 1mg of ammonia

Nitrite - produced from the aerobic oxidation of ammonia in the water

  • absorbed by the fish’s gills and inhibits the blood from carrying oxygen - hypoxia

  • toxic when nitrite level is above 0.10mg/L in soft water and 0.20mg/L in hard water

  • can be reduced by adding salt at approx 1 lb/100gallons or 0.12%

Nitrate - produced from aerobic oxidation of nitrite

  • the accumulation of nitrate will reduce the buffering capacity (alkalinity) of the water over time, which will allow the pH to decrease (become acidic)

  • relatively non-toxic to koi - they can survive at levels up to 200mg/L

  • koi do best if nitrate levels are kept below 20mg/L

  • high levels will stimulate an algae bloom

  • fertilizer for plants and algae

Alkalinity - the buffering capacity of water, which is the ability of the water to resist changes in pH.

  • Hard water reduces osmotic work required for fish to replace electrolytes (Na, K, Ca, Cl, P, bicarbonate) lost in urine. 

  • koi do well in water with a hardness of 100mg/L or more (tolerance range is from 20 - 300mg/L)

Biological Oxygen Demand - the amount of dissolved oxygen necessary for the breakdown of organic waste by microorganisms. 

  • the filter is biggest oxygen sink in a koi pond system

  • then the algae in the pond

  • then the koi get whats left


Brewster, Bernice, et al. Koi : A Complete Guide to Their Care and Color Varieties. Richmond Hill, Ontario, Firefly Books, 2015.

Saint-Erne, Nicholas, and Scholargy Publishing, Incorporated. Advanced Koi Care for Veterinarians and Professional Koi Keepers. 1 June 2003.

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8 Simple Tips For Creating A Healthy & Thriving Koi Pond


Tip # 1.) Clean your filter

Your filter is your pond’s toilet. It is best to get into the practice of back-flushing your filter as often as possible, even daily (approx. time 5 min), and manually cleaning your filter media (sponges, matts) weekly (approx. time 30min). If you are willing to put in a minimum of 1hr per week labour into your pond (6days x 5min. + 1 day @ 30min) then your will have a healthy pond for your koi with crystal clear water. They deserve it!

  • If you don’t have a filter, get one! Without a toilet/filter that you can clean/flush with ease your pond will eventually become toxic for fish. A filter is necessary for a pond with fish! 

  • There are many types of filters for your pond but choosing one that is well suited to your pond’s volume and bio-load and allows you to flush it easily is key. Bog and box filters are difficult to clean and flush away built-up debris. We recommend canister pressure filters for this reason. The Oase FiltoClear 8000 is easy to back-flush as well as to take apart and clean. Not forgetting to mention it has a built in 55w UV sterilizer (tip 6.)

  • If you have a pump on the bottom of your pond that feeds your filter, it is also necessary to clean it. The cage over pumps along with the impeller will clog with muck and algae over time. It is best to clean your pump no less than every other week. Weekly would be better. Your pump is the first stage in removing the debris from your pond to your filter so it can be flushed away. 

  • If you have an external pump with a basket strainer that sucks water from a bottom drain it will be necessary to clean the basket strainer weekly or as needed during times of heavy debris such as spring and fall. 

Tip # 2.) Add Oxygen

Top-down oxygenation may not be enough - meaning a waterfall or spitter. Adding bottom-up oxygenation from an air pump with an air stone or diffuser is almost always necessary. All living things, including the bacteria that are your pond’s biological filter, require oxygen. 

  • The bacteria in your pond’s filter will consume the most oxygen out of anything in your pond

  • Then next largest consumer of oxygen in your pond is the algae

  • Then your koi will get what oxygen is left          

  • Adding oxygen will provide enough dissolved oxygen in the water for everything to thrive

  • Adding bottom-up aeration will help to agitate & stir up settled debris so it can be picked up by your pump and sent to your filter

  • **A clean filter will consume less oxygen than a dirty one thereby freeing up oxygen for your koi. 


Tip # 3.) Monitor & Maintain your Pond’s Alkalinity

Start by testing your pond and source water’s Alkalinity (KH, Carbonate Hardness). Without enough alkalinity in your water, your pond’s bacteria are unable to convert the toxic waste (ammonia) from decomposing plant matter and fish excrement into nitrate, which is much less toxic to fish and is essentially fertilizer for plants & algae. 

  • If your source water has high alkalinity, in other words is hard water, you can replace the depleted alkalinity in your pond simply by doing a water change or by replacing the water lost from evaporation. This may be enough to keep your pond’s alkalinity levels above 100mg/L.


  • If you have hard water and top ups + water changes are not getting your ponds alkalinity to at least 100mg/L because of your bio-load (number of fish and decomposing plant matter), or your source water has low alkalinity, is soft water, then you will need to add a supplementary KH Booster.

Tip # 4.) Add Bacteria

 Bacteria are your pond’s biological filter and are essential for establishing the nitrification cycle in your pond. They convert the toxic ammonia byproduct from the breakdown of organic matter; decomposing plants, fallen leaves, and fish waste, into nitrate. Which is fairly non-toxic to fish and a fertilizer for plants and algae. 

  • Pond bacteria become more active when water temperatures are above 10ºC. 

  • There are cold weather strains of bacteria for the fall and winter months

  • There are various products that you can purchase to add the season specific bacteria to your pond. 

Tip # 5.) Add Plants

Plants remove nitrates from your pond and transform them into something beautiful to look at.

  • Annual pond plants generally grow more within a season than perennials and therefore will consume more nitrates within a season. ​

  • The removal of dead plants and periodic trimming back as needed is wise so as not to add more waste than necessary to your pond. 

Tip # 6.) Add UV Sterilization  

Ultraviolet sterilization is achieved by using a UV sterilizer. Which is essentially a light bulb that emits light in the UV spectrum, in glass tube that your pond’s water passes by. A UV sterilizer is extremely effective at removing the single cell algae that cause green water by clumping the small algae particles together so they can be picked up by your filter. 

  • Many pressure filters, like the Oase 8000, come with a built in UV sterilizer for maximum filtration

  • Also, there are external UV sterilizers that can be added inline to your pond’s plumbing. 

Tip # 7.) Add Flow

A still pond is a stagnating pond and frankly nothing gives ponds a bad name more than the smell of a stagnating pond. Stagnating pond muck creates hydrogen sulphide, a toxic gas that stinks and if reaches a high enough concentration in the pond’s water can prove fatal to fish. 

  • Listed below are some of the best ways to increase flow in your pond

    •  adding bottom-up aeration helps to stir up debris and turn the water over

    • adding a powerhead to your pond is very effective at creating more turbulence within the water and helps to dislodge debris that has accumulated under rocks (if you have rocks in your pond) so the waste can be picked up by your pump and sent to your filter

    • add another bottom pump to you pond with a hose that returns the water near the surface. This will help to turn over the water and stir up debris that has settled on the liner or underneath rocks, so your other pump or bottom drain can send it to your filter. 


  • Having a current in your pond also provides a play space for koi as they enjoy swimming against a current. 

Tip # 8.) Water Changes

 If you clean/flush your filter as recommended in tip 1. then you have done most the work when it comes to water changes. Simply topping up your pond with hose water after a back-flush or filter cleaning completes a small water change. Daily small water changes are ideal.

  • Topping up your water level from evaporation loss is not a true water change. If your source water is hard water, then it will replenish the lost alkalinity that is used up in the nitrogen cycle. However, evaporation leaves behind everything else in your pond but water, such as nitrates. Which will eventually build up and become more concentrated if not removed from the system by doing a proper water change.   

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