Hi All,
i have had some small koi dying gradually over the last few weeks.
about 6 weeks ago i changed my pump and added a filter to an existing system. Initially it was just two separate DIY box filters being fed by a submersible pump and filled with various media and led to two waterfalls. wanting to keep the helpful bacteria, i let the filter media muck up a bit and didnt clean it out. i changed my pump then a week later, added a uvc bio pressure canister filter thing before my diy filter box, still didnt clean the filter media as i wanted to keep all the bacteria.
i have 3 koi between 40cm and 30cm, about 20 koi between 4cm and 15cm and 12 roughly 10cm goldfish. ive had no issues with fish interaction, no strange behaviour etc.
about 2 weeks after changing the pump and adding more filtration i lost 3 fish, completely disappeared over night i was very confused as the day before they seemed happy and healthy with no adverse behaviour and so assumed it was a bird who had suddenly braved my bird hating dog and flew under my patio area for lunch. i haven't had a bird issue in 2 years since i've had the pond so figured it was a one off. two days later, another one missing.
this week, one fish was flashing excessively, i have had a fair bit of rain and it was right after feeding so i put it down to some water change and food crumbs in the gills, next day he was gone.
just today i have had another fish constantly flashing until he was too exhausted to swim. ive put him in a separate bucket with water, some salt and his own air stone to see how he goes over night.
since ive lost a few recently, im thinking the deaths are all related and the other fish have just been gobbling up the bodies.
i have had some minor flashing in the past after adding water but it always disappears pretty quickly and is random across the pond.
i realised my salt levels are probably pretty low to non existant. though water quality has been consistent and not shown any issues or changes aside form some heavy rain this week.
i have two waterfalls, some plants and two large disc air stones so i dont think oxygen is an issue.
i do not have access to a microscope or know anything about scrapes.
the goldfish seem unaffected.
Any ideas or suggestions?
Thankyou, your considerations are much appreciated.