Ever notice how many pond environment discussions end up addressing water changes or flow-through rates? The Bakki Showers discussion keeps returning to Maeda's 10% daily flow-through. The importance of alkalinity to a thriving bio-filter becomes re-inforcement for water changes. Build-up of nitrates, hormones, pheromones, etc leads to water changes. Ph crashes becomes a discussion of water changes.
No matter what filtration system is utilized, the goal is to minmize the deterioration of water quality that begins the moment the water is introduced to the pond. Some are fortunate to have source water that is useable without pre-treatment. Some need only de-chlorinate. Others may have sophisticated pre-treatment to eliminate a negative contaminant or to add a missing element. Once the water is introduced to the pond, we exert tremendous effort to keep it as close to that condition as we can, but it is always a losing fight. In the pond environment, water quality falls.
I just finished reading an article encouraging 10% per week water changes wherein the author goes on to say: "... or at least twice per month." This is the advice typically given to novice koikeepers ... the folks with the least experience in filtration maintenance, the least knowledge of water parameters and the greatest tendency to over-stock, over-feed and over-medicate. Repeatedly, however, we learn of highly experienced, successful koikeepers whose water replacement routines are at a much higher level ... Maeda's 10% daily flow-through for a lightly stocked, heavily filtered pond is just one example. The Japanese magazines are full of profiles of hobbyists at the top level who use continuous flow-through of that much or more. JR has shared his routine of multiple changes each week, with daily small changes through settlement discharge. Others have very similar practices. So, we find the elite of koikeepers generally performing far greater water changes than is recommended to novices ... the people who know the most and have the most sophisticated systems do more.
Sometime ago, somebody suggested water changes to improve fish survival rates. I suspect it was at the turn of the 20th century, when "science" and concepts of natural balance began to influence Victorian proclivities to possess and display nature in the parlor. Too many dead goldfish, minnows and exotic paradise fish rotting in a bowl for things to stay the same. Why 10% was suggested, I do not know. I suspect it was an amount that did not sound like too much work and was not so great as to shock captive fish that were weak. However it came about, the standard of 10% per week has endured. I think it terible advice.
At 10% per week, contaminant levels in the water will continue to build for a period of over 30 weeks before equilibrium is reached. [If it is ever reached.] Solid wastes may be removed mechanically or through settlement, but the non-solid wastes continue to be added and they "rot" in their own ways, whether it is through build-up of nitrates or decomposition of micro particles or dissolved organics. Hormones will impede growth. Immune systems are impaired. Excretion of waste chemicals through the gills and skin is less efficient. So, we tell newbies to do 10% per week, while the experienced among us do far more. They are the ones who need extra margins. It is the highly experienced who can race closer to the line.
But the highly experienced know better than to go close to the margin of their fish endurance capacity. They know the unexpected will occur, and that extra margins of safety (i.e., water quality) is essential.
Well, I've ranted enough. Think about it when next you advise the newcomer.