Nice, where abouts in NZ? Everyone that visits seems to think it is a beautiful place, but from what I've seen of Canada (that's where you are eh?) to me it doesn't seem all that special. That said, I love our mild climate and relatively low population, just a shame about the lack of fish!
19 years seems like a good run, I often look at the DIY projects on here and wonder how long some of them last, yours would certainly be one of the oldest I've seen. How will you know when the metal fatigue is at a point where the water level needs to be lowered?
I guess with the design even if you had to reduce the water level down to the bottom of the windows you could make an amazing terrarium above the water level and start keeping reptiles too!