[Auntiesue]

External pump for sure!! Maybe two especially since you should create 2 separate circuits in the event one breaks down for one reason or another. the other can maintain fish health until you make repairs on the other.

Basically you will need at least one bottom drain, a skimmer, a settlement chamber or vortex (or pond sieve) and some good bio filtration. I feel the hardest part of keeping a healthy koi pond is capturing the debris (including fish poo) and disposing of it easily. If you install good, easy to maintain, mechanical filtration, the rest is easy by comparison. If mechanical filtration maintenance is hard and time consuming to do, it won't get done and the fish will suffer. Include lots of air in your design as well. Koi thrive on a large amout of 02 in the water. Creat a system that also gives the pond a good current in the water. This will help your koi with body confirmation as well.

Here are a couple of photos of a smaller pond DH and I started last summer. Should have it finished this spring sometime (I hope)

Sue