The good, the bad and the ugly.
There are a few fundamental basics to Koi pond filtration as we see it.
The bad and the ugly.
Firstly, Koi pond filtration should never be pressurised. This includes sand filters, bubble bead filters, closed cylindrical type bio filters, closed 'black box' type bio filters and the like.Sand filters are about the worst possible thing to use as Koi pond filtration and anyone offering these up for a new Koi pond is in our opinion, way behind the times of modern Koi pond technology. No modern Koi pond should ever have a need for a sand filter anywhere on it. Ever. Same goes for swimming pool pumps - these are almost as ugly as sand filters.
Koi pond filtration should never be pressurised.
In other words it should be open to atmosphere - Such systems are typically gravity fed and pump returned, or pump fed and gravity returned.
Koi pond filter systems should always be 'open to air' so that you can literally stick your nose into the system and get it wet. These systems are either via a 'pump fed griavty return' design or, preferably by a 'gravity fed pump return' design. Such systems are flexible, radically more efficient, easier to maintain, have far lower running costs and can be fine tuned or adjusted to suit your specific requirments. Remember your Koi pond is being built to last for at leasy 20 years - your filter system has to reflect this.
They are more complex to install and require a fundamental working knowledge of a field we call hydrodynamics. You need to understand flow rates, gravity falls, pipe diameters, pipe runs, water circulation and you need an absolute knowledge of this thing called 'head'. In other words it is not simple - whereas just banging in a sand filter and a couple of sealed black boxes is very easy - a quick and soon to be very dirty installation.