Fantail deaths :(

[CometKeith]

Without beating a dead horse (fish) to death, they do produce O2 but only during the day so you were half right, at night they pull out O2 so it's really a reversible action in using CO2 to make O2 then the reverse.. Another factor we haven't discussed is water temperatures. Water holds less O2 at higher temperatures. That's why this problem happens mostly during hotter months. Also surface area of your pond is important. A lot of people determine bio-load by gallons but if your pond is deeper than the same size pond that has better proportions, the deeper pond will have less surface area gas exchange and will not be as well oxygenated. A lot of people think it's the waterfall making the O2 but really its having water movement as some people noted above. Thinking outside of the box and I have never read this anywhere but maybe... too many plants could hinder the water movement and decrease the O2? Anyone agree with this?

 

[callingcolleen1]

Yes Keith, it is true that too many surface plants such as floating plants, and even water lily's can grow so thick that they too can smother the pond as well, trapping deadly gases and not allowing for proper oxygen exchange. This is why I choose to grow mostly sedges, cause they grow upright and shade the pond as well as they clean the pond very well even in the early spring as they start to grow.

But in this case, it is just his fantails that died, so I was thinking it could be true that they were bred to death, as I have seen some strong male comet goldfish chase the poor females fantails to the point of being exhausted. In this case it could be that the balance of male comet goldfish and maybe the females are mostly the fantails and they can get overwhelmed in some cases.

If on the other hand it was just the largest of the fish to die, then it could be most likely caused by low oxygen and high build up of deadly gases.