This what we do in Australia Taken from
Reefing the Australian Way
I have running my setup for 9 months without missing a beat. I just only now need to remember to fill the top off tank about once every week or two.
The Front
the innards of the Box
We use the instructions from the
ATJ's Marine Aquarium Site - DIY - Auto Top-off II
The Peri Pump

The ones we are ordering are from
Williamson Pumps in the UK and will self prime up to 5 metres and are capable of 10M head pressure.
I hope this helps
skippy