I think for a new pond 5/8" is acceptable. More than in inch is not. It also depends on how deep the pond is, and how much flow you get back into the pond to replenish the loss. You may find over time as things settle that your losses will slow, and be even more acceptable.
In my case I was loosing about an inch per day when the pond was new and I had no inflow. Now the pond dam seems to have settled some, and the loss rate is lower, though I don't know how low yet. The inflow has not yet stopped.
