Koi & Goldfish Health Alerts

3 minutes read

We have since late winter been experiencing water temperatures fluctuating between 50º F and 55º F. If it’s cold we want the water temperature to stay below 45º F. If it’s warm we want the water temperature to stay above 65º F. This dangerous zone in-between desirable water temperatures is playing havoc on the health of our fish.


Now, since water temperatures are warming a bit we are beginning to feed the fish and the fish are becoming more active. That’s creating waste in our ponds. Nitrobacter, the good bacteria responsible for turning harmful nitrites into harmless nitrates (fertilizer), only develops when it’s warm. This means we don’t yet have all the cogs of the nitrifying cycle in place.


In the nitrifying cycle waste becomes ammonia which is harmful to the fish. The good bacterium, nitrosomonas, is responsible for changing ammonia to nitrites. We know right now at the store nitrosomas is growing strong in our filters and doing its job because our water tests indicate nitrites in the water but no ammonia. That means it has changed the ammonia to nitrites. But — nitrites in the water is not good at all! Nitrite tests done now at our store indicate a high nitrite reading. It doesn’t surprise us because it is not warm enough for nitrobacter to be strong in the biofilters. When nitrobacter is present in the system it changes nitrites to nitrates and completes the nitrifying cycle.


Alert #1


  • Now, more than ever, testing your pond water for ammonia and nitrites is crucial!
  • If you find ammonia and/or nitrites in your pond water:
  • Make water changes as necessary.
  • Cut back on the amount of food you feed the fish until the good bacteria set.
  • Add bio-building products such as Bio-Seed and MicrobLift.
  • Test the water daily until tests are consistently in line.
  • Add or increase the amount of bio-filtration.
  • Add non-iodized salt to help counteract nitrite poisoning.


Another problem we are facing at the store is an increase in the number of fish who are getting bacterial infections showing up as ulcers and/or fin rot. This we can also attribute to the water temperatures being between 50º F and 55º F for prolonged periods of time. The good bacterium, Nitrobacter, may not be able to take the cooler waters but many of the bad bacteria thrive in it. So — we have a lot of pseudomonas and aeromonas floating around just looking for an opportunity to cause damage. The opportunity presents itself in the form of low immunity in the fish. Koi and goldfish are controlled by water temperature. Their immunity systems do not fully kick in until water temperatures reach 70º F.


Alert #2


It is extremely possible that an otherwise healthy koi or goldfish may get ulcers and/or fin rot during this transitional time.


Here are things to do to prevent and treat for bacterial problems:


  • Perform a potassium permanganate treatment. We recommend this treatment very cautiously. This is something we do at the store but are very afraid of telling others how to do it because there is such a chance for overdose. It removes all surface bacteria on the fish, sides of the pond and in the pond water.
  • Perform a salt treatment. Salt gets rid of many parasites that can stress fish and make them more vulnerable to bacterial problems. It also naturally helps the fish produce a heavier protective slime cost.
  • Feed antibiotic food. Feed all your fish only antibiotic food for two weeks as a preventative.
  • Large fish with large bacterial problems can receive antibiotics via injection.
  • Treat the pond with Melafix if you see signs of bacterial problems. It’s not a cure-all but it helps the fish defend itself.
  • Do not stress the fish any more than you must by netting it, etc.
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