I have a pure white Koi which is 12 " long (very big). It is with me for the last 10 years. I have only one fish in my Tank of size 1.0 m length x 0.40m x 0.40m. It is very active and healthy. Recently I notice that after 2 weeks it becomes tired and lies down and then I can see the colour of the body and fins change to pink. I immediately change water . Half tank only. Then it becomes active again for 2 weeks.
1. I removed all the stones in the tank to make sure that no dirt gets accumulated under the stone. Not a single dirt in the Tank now
2. The heater is kept at 26 Deg C".
3. Placed additional air filter and Filter. Now 3 Air filters are working.
4. I feed only once a day with KOI STICKS
5. Did not check the PH level or Oxygen levels yet.
My house is Air conditioned and the average temp inside is around 22-25 deg.
Still this scenario happens every 2 weeks.
Can you suggest why ?
Thanks in advance for your advise