Gravity return pond filter and pump
A Gravity Return pond filter is the the most common and simplest type of filter you can get for your pond....but actually can also be the biggest and most complex but we will get onto that later. They basically consist of a filter box which sits outside of the pond and are fed by a pump within the pond.
Water is pumped up from the pond into the filter where it then simply passes through the various types of filter media and returns to the pond under gravity. The only requirement for this type of pond filter is that the outlet is higher than the return point in to your pond.
The advantage of this type of pond filter is that it can be scaled to a much bigger size than the pressurised filters so is ideal for koi or heavily stocked ponds due to the high waste produced from them. They are also very customizable not only regarding size but also the type of filter media that can be used, including bits of foam, plastic or other more specialised materials or muds.
DIY and customise your Gravity return filter
You can even have a go at making your own filter from a plastic box and other bits and pieces for the filter media. Go to a shop and have a look what filters can be purchased, you might be very surprised how simple there construction is. The pump is also something you can customise by increasing or reducing the flow rate. You can even connect one pump up to two filters etc etc.