Math,
I don't agree about the plants. In general you will find that ponds with a "plant filter" have a much lower ORP than those ponds with no plants. I know that within Holland many people choose plant filters believing these will absorb nitrogen compounds from the water and thus lower nitrate levels and improve water quality. It is a belief one often will find in those just starting out with koi of those stuck in one place in their knowledge of how a pond should be kept. Many people disagree with me and the battle to convince them is one I usually lose. The truth is most people with plants don't want to hear anything other that the fact that they are doing it great. I don't agree but what should I do, twist their arms until the admit I'm right? Of course not In the end we are all free to believe what we wish be it true or not. If you want a plant pond, I say why not? I just wouldn't put koi into that water. If you look about you will see most folk with hi end fish and much experience don't have plants either. There is a reason for this!
At this moment I am crunching some numbers and hope to come up with some calculations as to how many kilos of plants it would take to convert nitrogen waste of an average fish in a pond. The sums aren't finished yet but I believe it will be closer to 100's of kilos than 10kg.
I will be posting this on
http://forum.nvn-koi.nl/index.php?topic=5953. in Dutch if you want to follow it.
De mazzel
B.Scott