pond water quality

Experienced koi keepers are often heard to remark "We are keepers of water". Of course water is the environment we keep are fish in and consistently good water quality is paramount to maintaining fish health

Without a regime of regular water parameter testing, you will not be able to detect issues in their early stages should they arise. Early detection allows you to take preventative action and restore your ponds water quality to ideal conditions before fish issues occur. If poor water quality parameters persist, fish can ultimately perish
water molecule

Water Test Kits & Meters

Buy a complete WQ test kit which should include reagents to test pH, ammonia, nitrite, GH and KH. These are the most important parameters to test. Also deserving strong testing consideration are Salinity, ORP, Oxygen content and Nitrate. Test kits derive results by mixing reagents with the pond water. Add the required number of drops as directed and compare colours with the provided colour charts to determine if you have problematic levels

  • Excellent Nitrite levels. Hold the vial right to the card
  • Poor readings. Salt will help keep the NO2 out of the blood stream
  • Serrious Nitrite issues which require immediate attention

With some tests such as GH [general hardness], a simple titration is performed to an end point [colour change]. It's important to realize reagents have a shelf life. pH is purported to last the longest at about 2 years, but readings from other reagents this old cannot be taken as accurate. Bottom line, purchase a fresh test kit every year - far cheaper than medications and replacing lost fish

Pond Salt Meter
Salt meters are a highly recommended purchase and will pay dividends. Managing the salt level in your pond is very helpful. For example, you may want to maintain a 0.05% level during the Summer months. For Winter, 0.15-0.20% is preferred to reduce the osmoregulation drain on the fish. If fish have large ulcers, a 0.50-0.60% level will reduce the gradient between fish and water to help slow bloating

ORP Meters

ORP meters [oxidation reduction potential] are also popular with the more serious enthusiasts as they provide an accurate snapshot of your water quality. The higher the reading, the greater the oxidation potential [reaction potential] and therefore the cleaner the water. Abundant organics, low dissolved oxygen and poor filtration will reflect a low ORP reading [<200 mv]

ORP meters are also very useful in the correct dosing of Potassium Permanganate, particularly for the 2nd. and 3rd. treatments when properly judging the water colour becomes difficult

Nitrification - The Key


NH3, is produced predominantly by fish but also from decaying matter. It is toxic in even minute quantities [0.25mg/L] - damaging gills and skin, red blood cells [oxygen carrying] and increasing osmoregulation demands. It is far less toxic in cold water [2-3x] which is natures way of allowing fish to survive during the Winter when nitrifying bacteria do not function. As an ion, NH4+, it is not toxic. Because a higher pH has fewer H+ ions available, less NH3 is ionized into Ammonium and therefore there is more free ammonia. This explains why TAN [Total Ammonia Nitrogen] toxicity is a greater problem with higher pH levels as fewer H+ exist to bind with NH3


NO2-, nitrite can be a stubborn problem as it takes some time to cycle - 8 weeks or more. These bacteria require warmer temperatures [15 celsius+] and grow better in higher pH and lower salinity. They also require phosphorus to form ATP and fix Carbon Dioxide to obtain their carbon. I have seen effective NO2- conversion at temperatures as low as 12 Celsius with established filters. Nitrite poisoning is referred to as methemoglobinanemia or brown blood disease - the blood does not carry oxygen very well. This sounds bad and it is, we can see the effects of nitrite exposure several weeks down the line

NO3-, is far less toxic than NH3 and No2- as it is has minimal uptake by the fish. It is however, an immunosuppresentThese typically low level chronic conditions wear away at the fishes constitution by challenging the immune's system. The weakened fish is then more susceptible to more severe pathogens which can lead to a disease state and even sudden death. It also slows growth, promotes lethargy, jaundice and even blindness with extreme levels. Tap water in our area already has a reading of 12.5 mg/L nitrate. A level of 50 ppm is not ideal, but not of a great concern either

What Should you do when you have bad water quality ?

Maximize Aeration

Ammonia and Nitrite interfere with gills and the bloods ability to carry oxygen so maintaining a high percent saturation level is key. Of course the warmer the water, the lower the 100% saturation point is and their is a higher demand for oxygen by our fish

Add Salt

The increased ionic strength of a solution [in our case water] helps turn ammonia into ammonium [non toxic] as well as limit the amount of NO2- getting into the blood stream. Levels of at least 0.12% are desired, 0.20% is a good target with higher levels of NO2 . This is not a cure but can buy some valuable time [ approx. 1-2 months]. Essential the NaCl disassociates freeing the chloride ion to enter the fish instead of the assimilation of the nitrite

Remember, salt levels greater than 0.10% can start to damage sensitive plants like hyacinths and salt does not evaporate. To manage salinity levels properly a salt meter is required

Reduce Feeding

Feeding fish directly increases ammonia production. About 40% is barely digested and higher protein foods will increase NH3 levels. Feeding 1-2x per week can be a huge help in getting bad levels down and switch to a lower protein food

Ammonia Binders

We use CloramX and it instantly destroys ammonia. This is a great short term solution and is safe for the fish. Remember, with extremely high ammonia levels, these binders will be unable to tie up all the NH3 - but it will be much improved

Nessler based reagents will ignore the binder, giving you the same toxic readings that you had before the binder was added. Nessler reagents have brownish colour charts. Instead, opt for yellow/green colour chart salicylate based test kits which will account for the binder, giving an accurate reading

Increase Filtration / Reduce Fish Load

Fish release ammonia constantly when breathing, and 60% of the ammonia present comes from the gills. Increasing your filters capacity and / or reducing the fish load will have a immediate positive impact on WQ. Trickle towers & Rotating Media Filters are great filters, small pressure filters are poor, A stocking rate of 1 lb. of fish / 100 gallons is reasonable with a adequately sized mature filter, a maximum of 3 lbs. / 100 gallons is what we suggest. As an example, a 12 inch fish weighs about 1 lb, a 18" fish about 3 lbs.

There is a lot of misinformation regarding stocking levels on the net. Many suggest an "inches of fish calculation". This is the wrong approach. Consider the mass difference between 4 inches of fish when we compare one 4 inch fish to 4 inches of an 20" fish. The mass differential is huge, and that is what counts

Water Changes

I find that water changes don't accomplish a whole lot in terms of actual impact on levels. I have done 100% water changes, only to find nitrite levels marginally improved when re-testing just 5 minutes later. However, fish can actually store up to 30x the nitrite in their systems compared to what is in the water and I surmise this is released back from the fish after a water change - so some relief may exist. City water in Toronto contains 12.5 mg/L of Nitrate right out of the tap so removal of these less toxic substances is better accomplished with plants

Filter Bacteria Keys

Bicarbonates are essential for nitrification, along with plenty of 02. We already mentioned the importance of aeration, but maintaining adequate alkalinity levels is key. Using the tetra KH kit, you want to be at least 5 drops before a colour change occurs. This equates of almost 90 degrees german hardness which is a good level of buffering. Although nicer skin can be achieved with lower alkalinity levels, increased monitoring and skill is required to avoid a pH crash - therefore a <50 ppm content is not practical for most

Just add baking soda [sodium bicarbonate] for a quick boost in KH, but be mindful of the potential pH change. 1/2 cup per 1K gallons will increase pH 0.5 pt and KH at least 1 degree hardness [1-1.5 drops with the tetra kit]. So if your pH is 7.1, you do not want to add a lot NaHCO3 at once because the pH will change to rapidly for the fish. Sodium Bicarbonate will ultimately buffer your pH to 8.4, whether it be higher or lower than this figure

Managing Temperature
Being over 21 [70 Fahrenheit] is great for bacteria growth and the koi's immune system. Be careful however, because warmer water increases the toxicity of ammonia, as does a rise in pH. So there is a balancing act required, getting the water warm enough to encourage bacterial growth and conversion but to also manage the toxicity increase of NH3. Established systems with bio convert down to 13 celsius even though nitrosomonas prefers warmer temps of at least 15

Bio Seeding for New Pond Syndrome

It is a normal process for a new pond to experience spikes in ammonia and then nitrite. It may take 8-10 weeks for the cycle to complete and decent WQ parameters to be recorded. It will take years for the system and media like kaldnes and japanese matting to fully mature

I do question the efficacy of bugs in a bottle. It seems to be very hit and miss and certainly not validated as clients do not employ the scientific method when dosing. The best results come from capturing the dirty water that results from squeezing out seeded filter media ie. sponge, from an established filter system. This brown water is then placed in your filter, with the filter turned off. Nitrifiers are sessile, so allow 20-30 mins. before turning your filter back on. I have observed good results with this method fast tracking the maturity of a new filter

Let the Water go Green
Green water is probably the best way to help with poor water quality so turn off that UV. It is often stated that pulling the UV plug is done to stop killing bacteria - some merit I suppose although nitrifiers are bacteria that attach to surfaces, they are not free floating. If they are not planktonic, then they will not go through the UV

The main reason you want to encourage algae is because algae consume not only nitrates, but ammonium as well. There is a equilibrium that exists [NH3 + H20 = NH4+ + OH-] between ammonium [NH4+ an ion safe for fish] and ammonia [NH3 a toxic gas]. As the algae consume ammonium, NH3 is ionized to harmless NH4+ to maintain nitrogen equilibrium. Not only is the ammonia is dramatically reduced, there is a corresponding reduction in nitrite too because NH3 produces about the same number of molecules of NO2 during nitrification

We Perform Complete Water Testing at the Shop and on Service Calls

Water quality can go bad quickly, that is why we test our own tanks in the shop at least every 2 weeks. Remember, levels can be toxic and yet the fish will appear fine - but no indefinitely. When the fish show you there is a problem ie. clamped fins, lethargy, not eating etc. then the situation is advanced