Why are my pond fish dying?

We're trying to create a natural fish pond (we don't have the means to run electricity to the pond). About 5 weeks ago, we filled up the pond with hose water, let it sit for a week, then planted some lily pads -- they cover about 10% of the surface. about 4 weeks ago, we bought about 15 small comet goldfish. Since that time, they've died, a few per week. I've only found 4 "floating up" dead, but I don't see any fish activity in the pond anymore. They just went missing. We also put in a mosquito dunk because the water isn't moving -- but they aren't supposed to harmful to fish. Any ideas?

Why are my pond fish dying?
Hi. There could be a couple of factors. The mosquito dump is certainly suspicious, but they claim that they are non toxic. I would remove it anyway as your fish will sort out any larvae for you.



I think the most likely explanation is either that the pond did not cycle before adding fish - although with 5 weeks this seems strange - or that your oxygen levels are way too low.



You really need to get some water movement and a biological filter going. Consider a solar powered pump off eaby if you have no other choice. If your pond has a low volume only a few fish can be kept in stagnant water and your stocking level may have been too high.



Also get a water test kit and check ammonia and nitrate levels. If you do have a cycling problem then the ammonia will be high. If so, you will have to change a portion of the water every week until this settles down.



One other possibility depends upon what the pond is made of. If concrete, the water will be hard and alkaline as the lime is still leaching from fresh concrete. You will need water changes and a liner. If you used a sealant this could be poisoning your fishy friends. Again, a liner may solve this although it will be a major PITA to install now you have it planted.
Reply:Is a mosquito dunk a chemical thing to keep mosquitos from breeding? Dont worry about mosquitos, goldfish love the larvae so it wont be a problem. I think it might have made your fish sick. Also, the oxygen level might be too low for the fish. If you can get power to your pond to run a good filter system, then at least leave the water hose on just a little bit to keep the water from becoming stagnant. Good luck to you.
Reply:most likely high ammonia levels-ideally you should have a filter if you want to keep fish. other than that buy a water test kit and add a lot of oxygenating plants and wait until the ammonia levels are zero before adding fish-also use a dechlorinator as some tap water has chloramines that need to be removed