Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Well, 400 (American) gallons (333 Imperial gallons) sure puts it into the 'pond' size for filters and such.
Would you want to go further in that direction?
Drain the water via gravity to a long narrow channel.
Plant the channel with emersed aquatic plants.
At the end of the channel have the sponges or whatever other media you want (or need) to keep the pump clean.
Pump the water back into the tank.
This creates more interest in the garden, too. The channel could be part of a patio or deck area, could be worked into a bridge over a path concept, or even an aquaponic vegetable set up.
The basic idea is this:
Golds and Koi are very hard on plants.
Plants are a natural and very efficient filter.
By routing the water through a shallow (perhaps 12" deep) channel you can grow plants that get their CO2 from the air, so are more efficient than underwater plants at removing all the things we want removed from the water.
The catch is this: What will grow there in the winter? Will it freeze? The fish are not very active in the winter, so there is not really much waste, so maybe the channel could be shut down then, plants (kept in pots) moved to a place that does not freeze, but where they can be dormant.
An aquarium kept outdoors through the winter will get a lot colder than the same volume of water that is in the ground. Will the fish be OK?