After much thought I am making a lightweight box cover out of 1220x610mm 4mm sheeting, can get 10 sheets delivered of ebay for £41, make wooden frame, half of the lid will be left loose in frame so will just flip back and rest on the other half, sound as a pound. will be the 610mm high.
Pond:7500L, gravity fed POD, 11000lph to aerated 60l K1, 55w UV, elecro 3kw heater, 4 kohaku, 2 tancho, 3 sanke, 4 showa, 2 shiro utsuri, 1 goshiki, 1 Kikokuryu