Hello,If nitrite was the only thing that was raised- then its likely its due to filter bacteria not having yet caught up with spring, and increaed fish feeding. But you should also check you have enough air going into the pond.
To avoid nitrite spikes in Spring, keep a close eye on levels and only increase the amount youre feeding when nitrite is low (under 0.1ppm at the most). This often means ignoring hungry mouthes begging at you!

 

Thanks.

I didn't find the right solution from the internet.

References:

- https://www.pond-life.me.uk/forum/viewtopic.php?f=27&t=16005

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