Loss of fish

[wizzasmum]

Following a huge thunderstorm and very hot weather, I just lost two large koi and 4 goldfish overnight. The pond was 20 years old with no previous problems. I’m just left with 3 goldfish now. The pond water changed from crystal clear to murky green within a matter of hours. Still showing normal levels on test strips. Filter, pump and air stones ok. Any ideas anyone. I’m gutted

 

[Tula]

Very sorry for your loss, 20 years is a long time and I'm sure you were very attached to them.

My first thoughts are low O2 due to hot weather and if the storm brought heavy rains, a change in PH?

 

[wizzasmum]

Yes I was thinking that too, although it’s not happened before. I was thinking the rain would be welcome but obviously not Its rare to get such hot weather in uk. Thanks for your reply

 

[RMaynard]

Maybe it rained hard enough to allow run off to flood the pond? Fertilizers or pesticides washed in?

 

[wizzasmum]

I can see where you’re coming from but it’s a raised pond, approx 3ft deep

 

[Lisak1]

When the biggest fish die first, you always assume it was an O2 problem. The fact the water turned green is interesting though... makes you think there was a swing in the nutrient level. Maybe a dramatic pH shift. Maybe a combination of all three.

How many gallons is your pond? What type of filtration do you have? Were these koi in the pond for the whole 20 years?

 

[WaterGardener]

What is the pH?

Do you have a KH test? KH is alkalinity. Rain where I live is acidic and it can drop the pH if there is not enough alkalinity in the water to buffer the acid. The pH crashes and can quickly kill the fish and the beneficial bacteria in the system.

 

[wizzasmum]

When the biggest fish die first, you always assume it was an O2 problem. The fact the water turned green is interesting though... makes you think there was a swing in the nutrient level. Maybe a dramatic pH shift. Maybe a combination of all three.

How many gallons is your pond? What type of filtration do you have? Were these koi in the pond for the whole 20 years?

It’s 800 gallons approx with biological filtration and air stones around the edge. Yes the biggest 2 about 12 and 16 inches went first followed by the others which were trying hard to stay upright before dying I read that lightening can affect the nitrogen level rapidly

 

[wizzasmum]

What is the pH?

Do you have a KH test? KH is alkalinity. Rain where I live is acidic and it can drop the pH if there is not enough alkalinity in the water to buffer the acid. The pH crashes and can quickly kill the fish and the beneficial bacteria in the system.

I’ve tested the water with these strips and all coming back as normal range. Out tap water here is very alkaline but not sure if rain water, I’m guessing similar.

 

[wizzasmum]

I’ve tested the water with these strips and all coming back as normal range. Out tap water here is very alkaline but not sure if rain water, I’m guessing similar.

 

[wizzasmum]

Not sure if pic showing

 

[wizzasmum]

Another thing I’m wondering about is a cherry tree my neighbours planted a few feet from my house several years back which is now as tall as the house and overhanging the pond. After the storm I had to remove lots of dead leaves and cherry pits. Now wondering if they contributed and if I need to give up on pond after so long

 

[WaterGardener]

Testing strips are not very accurate. The liquid tests are better.

You could use shade cloth to put over the pond. It's the cloth that is used over greenhouses in summer. It comes in white or black and it still lets in rain. It doesn't cut all the light, so enough gets through for your plants. I suppose that would be obvious since it's for greenhouses.

It's also a small weave that won't let any debris through the cloth. It would also help with algae growth.

 

[Lisak1]

At 800 gallons with two good sized koi plus goldfish, you were seriously overstocked. Basically a disaster waiting to happen. Any small thing could have pushed your pond over the edge quite honestly.

 

[wizzasmum]

Testing strips are not very accurate. The liquid tests are better.

You could use shade cloth to put over the pond. It's the cloth that is used over greenhouses in summer. It comes in white or black and it still lets in rain. It doesn't cut all the light, so enough gets through for your plants. I suppose that would be obvious since it's for greenhouses.

It's also a small weave that won't let any debris through the cloth. It would also help with algae growth.

Thank you I will get some, makes sense