This is actually a serious suggestion.. If you live close enough to the ocean to pump in sea water, why not build something like this.. There used to be an attraction in the Bahammas called Coral world. It had a bridge to a tower out in the ocean, where they made an artificial reef that got populated by local sea life. It was amazing, and no water changes, chilling, etc.. All you'd have to do is maintain the structure.. Attaching a picture. There was a viewing room underwater.