Question: asked about lack of oxygen in fish pond resulting in death of fish
Answer: told him to do the following things -
1. cut the trunk of the banana tree in one or two part in round shape and apply it. 
2. apply potassium permanganate or potassium crystal for 250gm for half a bigha pond in one day interval.
3. apply agrilime (calcium carbonate) at 5kg for half a bigha of pond