Question
Hello,
We have a 90 gallon pond in our backyard.  For the past two or three years, we have had a frog (or toad, not sure) that always finds a mate, and we end up with tadpoles.  They seem to help keep the algae down and are fun to watch.  Well, about four days ago, we had three pairs of frogs laying eggs.  They were everywhere, attacked to the plants, on the rocks, etc.  We joked about whether or not there would be enough room for all of the tadpoles when they hatched.  Well, they hatched yesterday, and when we got up this morning, all of our fish (three large goldfish and one koi) were dead.  The water was very green (it had been pretty clear before the hatching).  Was it the tadpoles that killed our fish?  There must have been hundreds of them!  Thanks.

Answer
I'm so sorry about your fish.  The tadpoles may have caused their deaths indirectly.  The shear number of tadpoles could have raised the ammonia or nitrite levels up.  Did you test the water for those (and check pH too)?  Since you had those four large fish in there, there was already a lot of waste products from them.  Add on the tadpoles, and it was too much.  Another possibility with overcrowded conditions could be low oxygen.  You can buy an oxygen test kit. What kind of aeration and water movement do you have?  How hot is it there?  If it's hot with the water temperature at or above 80 degrees F, then I would say that oxygen was the problem.  

Fish sometimes eat tadpoles.  They shouldn't get sick from that unless they ate cane toad tadpoles (found invasively in Florida and Texax).  Other toad tadpoles would make them sick but rarely kill them.

You might want to consider making a larger pond for fish and leaving the 90 gallon pond to the tadpoles.  Koi should have ponds of 1000+ gallons.  Goldfish should ideally have at least 100 gallons for a few of those as well.

I wish you and your fish better future luck.  

Robyn
fishpondinfo.com