Everything had been going fine since March (when we started the pump)and the pond was becoming clearer and the free of debris etc. All was ok until last week, when in the space of just 36hours the pond dropped by about 3-4". The previous owner had told me in an email that during the summer he regularly left the tap on to spray a little water in just to keep it topped up. Knowing nothing about ponds I assumed that was an ok thing to do, but now a friend has warned me of the dangers of chlorine etc in tap water - although he believes it's ok to alter upto 20% of the pond with regular tap water at any one time without causing harm to the fish.
I can't seem to find the definite answer I'm looking for as to whether leaving the tap on overnight every night to keep the pond 'topped up' is an ok thing to do? The pond itself is very clear at the moment - I can pretty much see the bottom. The fish appear to be ok, although the last two days have seen a sudden drop in temperatures where I live and I understand that may be why they've not been fussed about feeding and have remained near the bottom of the pond.
I don't have the foggiest as to how I go about locating the leak and fixing it!!!

I would really appreciate any helpful hints and tips.

Thanks

The first thing you need to do is check all your conections from pump to filter, the filter it self, then the return to the pond, a 3-4" drop is a huge ammount to lose in a short time, and most loses such as that happen from leaking joints or connections, or a blocked filter that over flows.

If you have a waterfall look closely at that, plants can grow quickly and cause water loss over the sides, but large water loss quickly is always a leak somewhere, you jsut have to find it, in dry conditions its easier, you look for a damp patch, but after all the rain we had you will have to look closer.

having followed your advice, I've checked the stream and all connections and can find no obvious cause for the leak - so I'm pretty sure there's hole in the pond liner. My pond has a 3ft high brick retaining wall at the far side (our garden slopes down the hill) and there are no signs of water there, so I can only assume the leak is escaping underneath the pond.
I need to find and fix this leak, as topping up from the tap is not a viable long term solution, but where do I start?

Firtsly, I'll need to find a suitable safe place for the 30-40 fish (some of which are upto 20" long!!) - any ideas? I'll need a pretty big paddling pool!!
Secondly, do I forget the leak in this liner and lay a new one over the top?

oh the joys...

thanks again.

If you need to put in a new liner, I assume it would be better for the fish if the weather is cooler rather than warmer....but I don't have "proper" fish so I'm not an expert.

ps do you have any photos of the pond you can upload onto the gallery?

will try and get some pics this weekend and upload them.

as for moving fish in warmer weather, its better to do so if you can work fast and have a decent sized holding place while you work, you may lose one or two through stress, but you would probebly lose more long term by adding so much fresh tap water all the time, laying a new liner on top of an old is a matter of choice, some say yes some say no, personaly i have done so in my small pond, but wouldnt in my koi pond.