| Using potassium permanganate as a cleaning tool has consequences you may not intend, such as elimination of the biofilm, nitrifiers and algae that give a mature pond the ability to withstand external impacts that could otherwise devastate the bio-community on which our fish depend. PP is indiscriminate. If 100% of all "bad" microbes are destroyed, 100% of all beneficial microbes will be destroyed. You are then at a start point of breaking in a "new" pond, and new pond syndrome will be your challenge. In a cool climate, it could be two or three months before nitrifiers are established and the full biota often takes a couple of years to establish. An annual PP "nuclear war on microbes" may result in you never achieving the mature bio-environment you want to achieve.
I would suggest you and your koi will be much better off by physically removing any debris and engaging in water changes to the extent needed to have proper water quality. After physically removing the debris, there may be some mulm left that is too difficult to net out. (I used to lower the water level to wading depth and use a 6" fry net to capture any debris, since it would capture all but the smallest particles). To get that last bit of mulm, before using PP, consider one of the "sludge buster" type bacterial concoctions. These "bugs in a bottle" potions do work, particularly if most stuff has been physically removed first. These harmless bacteria will competitively displace some of the harmful bacteria involved in decomposing waste. Using these products is a crutch for dealing with a problem best addressed by good design and regular maintenance, but when a need exists, they can help.
I do not believe there should ever be a need for a "spring cleaning" in a properly designed pond, because the bottom drains should have picked up any appreciable amount of debris/sediment. But, I realize we all have to deal with what we have, which is often not as well-designed as we would like. |