Question: Dr. Novak, I built an Anoxic filter for my 3000 gallon pond last spring using your design, took a while to get going but once it did it kept pond clear all summer. My question is: What do I do in the winter when it gets below zero. Do I just drain and clean the bottom of filter, cover it for the winter, and just fill it and start up early March?
Well, here it is that time of year again when either the decision has to be made to keep your Anoxic Filtration System (AFS) running all winter long or close it down and let it freeze-up until next springtime arrives.
With conventional filtration systems if the decision is made that the filtering system has to be shutdown then that means you will have to inoculate the system all over again in spring with vital bacteria cultures once again. This then becomes a very trying time for the fish and hobbyist in that the ammonia intensities along with Nitrites will begin to increase to uncomfortable levels for our animals that sickness and even death may be its outcome. In early springtime Koi do not need any more stress placed on them than just trying to adjust to eating solid foods once again and building their immune systems back up to acceptable levels.
In natural systems this whole restarting of the nitrogen cycle does not present a problem for the animals in that system like our closed systems do. Why you may ask? Because natural systems work off of the same principles as the AFS does. There is an abundant supply of heterotrophic facultative bacteria in that system that just adjusts to the available foodstuff and temperature so quickly that the animal life goes on about their business without the “nitrogen cycle stress” that we as hobbyist put our animals through.
In very cold climates like we get in the Midwest USA and Canada temperatures may dip so low and far so long that even if a heater is added to the pond freezing of the pond is still inevitable. Wouldn’t it be nice to have a filtration system that even under such demanding conditions of the coldest winters that the filter would automatically spring back to life once again? Ammonia spikes would be a thing of the past, right? The AFS is just such a system that does exactly just that! It can freeze solid and still come back to life after the coldest of conditions have past, not so for conventional systems. I’ve added some links to help those that may want to educate themselves in better understanding the AFS and cold weather and why conventional filtration systems die in such harsh cold conditions.
The three photos show why my pond has to be covered by the end of September. Bird droppings along with leaves from the Crabapple tree and its half eaten apples by the birds are insults that will degrade water quality if not contend with.