You've made things a little more difficult for us than it should be really. Your other thread, "fish for pond" partially addresses some of the issues which are also pertinent to this thread. It would have been better to keep it all under one thread!!
You stated one very important fact in that other thread, and it speaks volumes to me. You said that no one in Saudi has ponds, they're just not a done thing. There's a very very good reason for this...summer temperatures!
They are brutally hot in Saudi, having a pond is crazy when you think about it. You are currently trying to deal with problems that lots of other people have probably already tried and failed with, hence the lack of ponds over there!!
And then on the flip side, even though your winters are relatively mild, the night time temps are uncomfortably too low for most tropical fish. These are the problems you are faced with.
In summer I suspect your pond needs cooling, with lots of added water agitation too to compensate for lack of oxygen levels. And in winter it needs a heat source.
The ideal solution would be to have your pond in an enclosed room, and actually control the room temps. Air conditioning would probably be the best way to achieve this though what your energy costs are like over there I don't know. You'd have to have it on constant cool during the summer, and warmer during the winter.
Or maybe you need to give up on the pond and just go the aquarium route, which you already have to a degree.
