dan what i would be worried about is damp in the conseratry and are you building another wall against the conservatory for strenght, and if you are keeping the pond at two levels i would put both your drains in the deep end , and put two returns at the shallow end so it pushes the debrib and waste food down to the drains, and then put the final return in the deep end so that it gives you a kind of vortex effect to get it down the drains , also put a skimmer in the deep end.then you could use the swallow end to feed so that you can see the fish real nice and the skimmer will not eat all the food straight away , but so far its looking good mate , | 
