When building a koi pond,I found that the only consistency is that things are constantly changing.....

Know that feeling all too well. Took me three years to finish mine...and its only 9000L.

I build ponds.
It takes me 10 days to build a 60 000 litre Natural Rock Koi Pond, complete with H.P. Bio System, Waterfall and ready for fish. (Weather Permitting.)

Dynamix

10 days? Concrete takes 28 days to fully cure. Could you please post some pictures of ponds you have done! Do they look the same after 10 years? Or is there a little maintenane involved

Eugene

I only use 30 MPa strength concrete. This is known as High Strength Concrete.
This is handpacked and cut and roughly finished to receive the final plaster finish.
Curing begins after the exposed surfaces of the concrete have hardened sufficiently to resist marring. Curing ensures the continued hydration of the cement and the strength gain of the concrete. Concrete surfaces are cured by sprinkling with water fog, or by using moisture-retaining fabrics such as burlap or cotton mats. Other curing methods prevent evaporation of the water by sealing the surface to retain the moisture in the concrete. The concrete will continue curing for 30 days to full strength. It continues to harden and gain strength over many years.
Not all concrete is sealed...if not... it must be cured with the wet sacks etc.
The casting MUST be completed in one continuous operation.
It is known as a Monocoque design.
As soon as I figure out how to post pics...I will show construction methods.

My ponds are built to last 20 years plus.
The sealant I use is plasticised and will absorb a lot of the earth movement experienced in Gauteng (Tremors)
Their are numerous other considerations that must be taken into account when building a pond.
I have learnt the hard way over the last 30 years and I will not change methods as they have proven themselves to work.