Pond Goldfish - One Dies Every Few Days

[V8RX7]

We have a large pond that the PO kept Koi in, we have had 40 4" goldfish in for 9 months without issue

For the last 4 weeks we are finding a dead goldfish every few days - at first we thought it was the Heron (we have netting) but they all appear unharmed

I've tested the PH which was ok

It does seem that the more I run the filter / waterfall the more die, there are no obvious signs there is anything wrong with the fish nor water

Any ideas ?

[Boosted LS1]

I know they've been there a while but could it be over crowded? How large is the pond? Also, could it be a lack of oxygen given the hot weather we've had?

[V8RX7]

I doubt that's the problem - it seems to be worse the more we operate the pump / filters.

It's approx 3m x 3m x 1m the PO kept around 30 18" Koi in it.

We have had a lot of frogs / tadpoles though.

[Turn7]

Get a water test done for NItrate,ammonia and NItrite.....

Latter two should be zero .

Possible decaying fish or frog polluting the water.

Any filtration system? If so check it all running correctly and not blocked or failing .

[Boosted LS1]

If the pumps been turned off for any length of time the filters could be full of dead bacteria. In which case you may be pumping poisons, pollutants into the pond.

[Jasandjules]

What are your water parameters? Have you a filter of any kind?