hello, I just came home and notice my sansai kujaku is having troubles with breathing and is barely moving. i have 19 koi in a 1200 gallon set up right now due to winter. i have a easy pod and a 55 gallon filled with k1 (cycled) on one pump, and another 55 drum filled with mechanical media going into a 65 gallon drum with more k1 with another pump. both pumps are external. my ammonia is 0 nitrite is 0 and nitrate a 20. currently doing a 20 percent water change every night. the temperature is about 70 degrees.
the kujaku is struggling to breath and swim. no other koi are showing any signs like this. he is also the smallest koi about 1/4 of the others even though we got them at the same time. right now he is staying behind the inlet to avoid the current. he seems very weak i can pick him up right out of the water without the use of a net. sometimes he has been doing a weird twitch to burst his head out of the water. another koi can also bump him and he just goes on he side, then corrects himself. i have noticed heavy breathing in the past and have done multiple scrapes and only noticed one fluke. we also run on well water the kh and gh are very high and the ph is at 8.2. we also currently have low levels of salt in there .07 ppm. does anyone have any idea on what is going on and how can i fix this?