Hi Austen.
The main flow through these pipes is going to be taken care of with stream-type pumps. I've had very good experience with Tunze turbelles, not least with my
streambank tank.
Electricity consumption is miraculously low compared with regular pumps. You just need to give them a roomy channel to cut down the end pressure. Heating the water is kept to minimum also.
I made two channels, 110 x 55 mm (4" x 2") each to give some playground with the pumps.
Testruns will determine whether I'll be running two pumps all the time or regulate the flow by either cutting one down during the night or maybe switching them on alternately.
Seeking for interesting options as we speak.
There's also going to be a secondary flow system, feeding the rock/wood scape and a couple of waterfalls/dripwall above the water.
I've got a couple of OR 3500s to play with.
Thanks for looking.