Recently I have been doing a lot of research on the possability of building a large indoor pond. I have been keeping small aquariums (a few 20-30 gal. & a 55 gal.) for about six years now and always dreamed of having a huge tank (200+ gal.). However, I met my fiance two years ago and she had two red eared sliders, both about four inches long, in a ten gallon aquarium. I informed her that they need to be kept in a larger tank, so we bought them a 40 gal. breeder. Since then they have grown to about six inches. This is what led me to desire an indoor pond. I could give them a large enclosure and satisfy my want for a large aquarium (hmm...maybe) at the same time. Like I said before I have done a lot of research on cost and how to build. However, I have been unable to find any information on what my electric bill might be for the equipment required to sustain the pond such as lights, filtration, etc. I am looking to build a pond that is anywhere from 1000 to 2000 galons and will probably by a filtration system suited for much larger than that since turtles are messy and I plan on keeping many large fish also. Can anyone give me a ball park estimate? Or offer suggestions for minimizing the cost. Will adding plants cut down on filtration requirements? Also would there be a significant difference in the cost for electricity between an outdoor pond vs. indoor pond? I appreciate any input and apologize for the long thread.