Simply Koi and More Koi

Hey there,

recently a friend of mine asked my opinion of koi food.

He has 5-6 koi in a small tank for about 6 years. He had always feed them very low quality koi food.
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He asked my opinin and I suggest to him a food that I use this time of the year which is very high in protein 44 percent and colour enchancer.

He feed about 20 pellets to them and after eating a few they did not eat anything else.

The day after koi started dieing.

I did some check up and he did not have ammonia , a little bit of NO2 and a bit of No3 which in my experience could not cause a massive death.

I also perform in scraping and gill microscopsy and could nto find a thing.

Could the immediate change cause this issues ? I told him to stop feeding it. and wait till fish are okay before continueing.

Water parameters are important when investigating a koi health problem. You say there was a little bit of nitrite, can you say what were the parameters, especially the pH?

yea NH3 was zero. no2 was 0.5 no3 was 0.5

I did not measure the pH, I should have, because I really see any problem with the pH in my country as it is too hard to change.

The guy had the fish for 6 years, he never had such a thing and by switching diet all this happened.

yea NH3 was zero. no2 was 0.5 no3 was 0.5

I did not measure the pH, I should have, because I really see any problem with the pH in my country as it is too hard to change.

The guy had the fish for 6 years, he never had such a thing and by switching diet all this happened.

The nitrite level was about 2½ higher than the normally allowed maximum level but that isn't high enough to kill koi, especially in the short term.

I've never heard of eating a few pellets of a new food being the cause of death but one possible idea is that there was a pH crash. I would need more results in order to prove or disprove the idea but my reasoning goes like this:

The high protein content of the new food would have meant that there would have been a higher than usual ammonia excretion from the fish or if uneaten food was allowed decompose. In the process of converting ammonia through nitrite and into nitrate, the bugs in the biofilter use roughly four times as much oxygen and seven times as much carbonate as the ammonia they convert. Ignoring the oxygen and just concentrating on the higher use of alkalinity due to the higher ammonia, that means that the carbonate reserve in a small tank could have been depleted very rapidly and that could lead to a pH crash. A pH crash can kill very quickly and deaths within a day are easily possible.

Of course, in the absence of more detail such as pH and KH values, this is pure speculation but it neatly fits the fact that the koi died within a day.