a little food for thought that I put together for another forum......
There are a few things you may want to consider before the shovel hits the dirt, and by consider we simply want you to think before you get started, ask lots of questions so you can build the pond that truly works for you and enriches your life.
These things work off of each other in determining the kind of pond you build.
Lets start with size. If you are considering keeping koi you are going to need a pretty big pond, most koi keepers agree a basic rule of thumb is 1000 gallons to start off with, and at least an additional 350 gallons per adult koi. This may be an issue in determinating the location of your pond, is there room? So you dont have enough room in the spot you have chosen for that large of pond then a smaller pond can happily support a nice school of colorful goldfish.
From another angle take a look at location. Perhaps it is a flourishing water garden in your dreams. Tons of colorful lilies, lotus and marginal plants! You know just where you want it too...but did you know to bloom most water plants need a mininmum of 6 hours of direct sun? so if colorful blooms are your heart's desire then reconsidering the location is needed if the shady side of the yard was where you were considering putting it.
Think about what you want to acheive from your pond, a quiet reflection, big colorful carp, a crashing waterfall? Ponds come in many atmospheres, but in basically 3 kinds. we can have a look at a brief summary of all three.
Water gardens are generally fairly shallow and still, plants like 18- 30 inches of water and of course marginal plants like to have just thier feet wet. Plants also prefer still waters. Though many water gardens have a waterfall feaure to them, lilies definitely stay clear of the splashes! Goldfish thrive in water gardens and are gentle on the plants. Some watergardens have little to no filtration and they are built in all sorts of sizes. Often there are shelves built in to the wall of the pond for putting plants at their favored depths. Generally there is a big spring or fall clean out of a water garden pond. The amount of sun this pond receives is a big consideration for location.
Koi ponds are built specifically to house koi. They are four plus feet deep, they run with good current to the waters, are large and heavily filtered! here is a good explaination from the Atlanta Koi Club
The controversial blended pond, despite the fact that there are many reasons not to put koi into watergardens, it is done and done often...thus the blended pond. The bottom line is plant and koi needs are on opposite ends of the spectrum. Koi LOVE plants, they are omnivores. Koi love to root in the mud and a 20 inch koi can easily root a plant from a pot and will have a grand time doing so. Plants need shallow waters and koi need deep. Koi thrive better in strong currents and plants of course do not. The debate rages on of whether the two types of ponds can/should be blended into one. The mix of types will take away from the koi growth and plant growth potential, but if that is your dream, so be it. Although more challenging to strike a balance with, there are successful blended ponds out there. If this is your chosen monster to tackle we can only promise to be truthful with our answers to your questions.