building gunite koi pond

There are also paint-on water based latex liners that can be directly
applied to concrete that seal out the lime that leeches back into the
water.

It's relativly cheap, looks a LOT better than a 'tarp' liner, and is
actually LEGAL in all 50 states. Out here in California there are a lot
of EPA guidelines etc... that make the toxic based illegal (not that
you should be using them anyway).

I've used them and their not much worse than plain latex. Liquid latex
uses amonia to make it set. It's a bit stinky, but it's not all that
bad compared.

If you want to know more, please drop me a line.