A couple questions about 4000 gallon pond? ( please answer)?

all tetra filters are great for any fish or reptile use and should do fine for koi or large goldfish. For digging the pond, it really depends on how many people you are working with. If you do it alone, then it shouldnt take more than a week. If you need to find cheap koi, try petsolutions.com or your local petsmart has smaller, younger koi for your pond. Best of luck, put up pics if you can.