I can’t remember how much of this I have shared here but I have really wanted a koi pond and it’s been a frigging struggle. I just tried to piecemeal the project with leftover supplies and my own efforts and it’s been a real struggle. I should have waited until I could just do it right. Last year for my birthday in September I bought myself a new liner to replace the leftover vinyl liner I was using that kept springing leaks. Literally, two weeks after I finally got everything going, we had a huge storm, the landscaping shifted, and a piece of slate I balanced as a waterfall shelf shifted and fell, and put a hole into the pond I have been trying to find for a frigging year. A week ago, I got invasive and disturbed the heck out of the fish by searching intensively, lifting up and feeling every frigging inch. Turns out the hole is FAR deeper than I realized. It’s been so hard to find because it’s basically at my yards waterline. But I found it and put a patch on inside and out! And finally, I have my pond back and clean, just in time for the plants to die back for winter!
Thanks for reminding me of the drawbacks of having a pond in the garden. LOL! These are good reminders just in case I ever get tempted to put one in.
“I should have waited until I could do it right.”
I think we all have said these words to ourselves, some of us multiple times. But sometimes, you just can’t wait. 
Although, the times I have jury-rigged something together, and I’ve worked on it and worked on it, I find I really learn more about it than if I did it the “right” way to begin with, because along the way I’ve had to trouble-shoot a bunch of problems. I bet if someone came to you for advice about their koi pond, you’d be able to answer almost any question. Or if you ever had to build another koi pond, it’d be a darn good one. So there is an upside to all that work. 
I’m glad you finally found your leak and were able to fix it, and I hope you have many years of enjoying your pond in your future!
Gosh it seemed so simple in my head. Hard clay, leftover liner, cheap pump, fish poop in the water water the plants, huge veggies. On the other hand, the elephant ears down draining from the leak are frigging massive.