Funny you say that...I was out of town and my sister who was feeding my pond was going to be nice and top it off for me (she has had ponds herself). Well she left and forgot the hose running for about 4 hrs in a 300 gal pond. Needless to say I lost like 14 nice koi out of 18 total. I had just set it up so I had just paid for all the fish...some as much as 100 each and quite a few in the 60-70 range. Probably would have paid for that unit in dead fish
If you look around there are some maintenance free systems that you just install and replace every ten years. In the long haul they are a little more expensive but you have to do zero maintenance or up keep for 10 years.