Question: query regarding removal iron from pond water.
Answer: 1.immediately stop feeding and fertilizers and change the water @ 30% or give aeration using aerators if it is possible.
2. if there is no provision for replenishing the water or there is no chance for artificial aeration and if the water level is above 1m:  potassium permanganate @ 250 grams/ 0.1 ha and agitate the surface with bamboo. 
3. you can apply toximar @5kg/bigha to correct the water quality.