Thanks MWood for sharing the info. Love to see those pond tubs. Really like the plants growing on your wall behind as well. I am certainly going to look out for some H. zosterifolia now and will definitely try it in my ponds.I have overwintered it for the past 3 or so years, though I do admit that my garden is pretty sheltered and in London, I've chanced my arm with a lot of tender plants with some success (and some failure), mostly because of laziness. It did make it through the cold in 2018 though. It's in a basket with Darmera peltata, about 15/20 cm or so under the surface, in some Velda pond soil capped with gravel. However it often escapes and floats freely, or sinks and roots into whatever. In your setup I imagine it would be quite a sight! I've also got some Rotala, Hygrophila and Crypt wendtii in similar conditions out there, so we shall see... Potamogeton gayi also did well this summer come to think of it.
I have had A mentho outside for years, in tubs not much bigger than yours. And in huge numbers for such small tubs. They have a pond to themselves now. Hopefully next year I can catch some adults to breed and I can get you some eggs or fry. Yes, they prefer hard water and I cover the tubs with plastic in the winter which helps keeping the water from getting too soft because of the rain. I will post more about my fish soon.Great fish, A. mento very much on my list - do you have any problems with the rain making the water less hard than I understand they like?