Significant water loss in pond HELP!!

[splinternet]

Newt19 - I've got the same problem. My pond (oval shape, max width 2.8m, max depth 45cm deep, max capacity c.1500 litres, concrete build with no lining) has been in situ for about 20+ years, in shade about 50% of the day. I have a FishMate pump and filter. About 99% of the time throughout all this period, there has been only minimal loss which I would attribute to normal evaporation. However, the remaining 1% of the time suddenly sees alarming drops in the level, roughly one inch per day. This lasts usually a week or two, then normal service is resumed. There seems to be no rhyme nor reason as to when it happens; for instance, throughout this year's hot summer, I've only needed to top up about once a month after the level has dropped about 1-2 inches. But in the last week or so, it's suddenly started losing more than an inch a day. We were away for 5 days last week and when we got home the level (which I had filled before leaving) had dropped 8 inches. I topped it up again a couple of days ago feeling guilty in the current water situation, but it's still dropping at the same rate. I'm stumped as to why this happens. I've checked the filter and all pipework and everything is watertight. I rule out a leak thinking of my "99% of the time" plus the fact that the pond structure is mainly above ground level and there's no indication of leakage through the concrete walls. Have the meteorological conditions suddenly changed so much as to cause this much evaporation (general question to everyone)? I'll keep an eye on things over the next few weeks and if there's no change, I guess I must reluctantly conclude there's a leak

 

[Lisak1]

@splinternet - whenever there's intermittent loss, most would assume that yes, it's some change in the weather. Hotter, drier, colder, windier, etc. But 8 inches in five days? That's a lot. It almost sounds like a leak of some kind that manages to seal itself back up... maybe gets clogged with organic material or something? Just a wild guess! Post some photos - that's sometimes helpful with diagnosing where to look.

 

[splinternet]

@Lisak1 - thanks for your response. I've attached (I hope) four photos. You can see the "tide

mark" where I filled the water two days ago