Pond leaked out overnight

[Tincan]

Apologies for my slow reply. The overnight leaks have disappeared, Ive got a fountain as well as the pond pump running now so it is looking a lot better. I've fashioned a gap in the bog filter pebbles where the water mainly impacts the bog, to try and spread the waters depth coverage within the bog. The issue i now have is there is a slight drop in levels of the pond over 24 hours of running both filter and fountain, but it doesn't go beyond 10cm. No signs of tears in the upper liner, so I'm once again a doing lots of testing to see where it might be.
Im also now looking for a de-chlorinater as Im using tap water. Does anyone have any brand/volume suggestions?