What you should do to start an indoor Koi pond? How to build a koi pond? If you want to make a 300 gallon tank is to keep the fish indoors over the winter and that you have or will build koi pond outdoors for them soon. For your baby Koi fish will grow fast. Well, if given good water, good food, good filtration, they will grow to about 7-11 inches their first year depending on their variety and genetics. That’s the first year. After that they will double their size each year until they are about 3 years old. Then they slow down a little bit. I have a Koi fish in my indoor winter holding tank that is 32″ long with a girth that measures about 21″ around. She’s only 4 1/3 years old right now. You should take a little time and do some reading about these swimming jewels and you’ll find they need much care and lots of room to grow. So do not discourage your love for these creatures, but you would not be happy keeping these fish if you knew you were not caring for them so they thrive, not just survive. So you need large koi ponds for your koi fish.
For filtration, when you had a 300 gallon quarantine pond, you should use a 50 gallon barrel filter for that system. And let the barrel sat outside the pond. It was a trickle tower style koi pond filter system. That is a filter where the water comes in through the top and trickles down over filter media. Also you can use plastic ribbons in that filter and that will work great.
Something you should pay attention, you should not get a pleco. For it can become aggressive and hurt your Koi fish. If you think that they can do much to help keep things clean anyway. That is wrong, for you’ll need to feed them real fish food as well. And that means there will be more of a load on the system.
For a 300 gallon tank you would be suggested a koi pump that pumps at least 750 gph. The koi pump has a head that would be about 500 gallons per hour. For a good koi pump makes a nice turn over rate for the system. Also you need air stones. For Koi fish love lots of oxygen in the water and they thrive on it.
If you really like to make such a small koi pond, it is possible, but not suggested. It’s not healthy for them to live like this, for growth of your koi fish will be stunted most likely.
If you are new to keep koi fish, you can visit some message boards like KoiShack, KoiBito and Koiphen and read a lot. You can learn so very much from these message boards if you really want to keep koi fish and you will know how to build Koi Pond.