I don't know beans about Koi ponds, but cornmeal is a flour made from what you Brits, for some unfathomable reason, call maize.

Not unfathomable - "corn" is a derivative of the word "kernel", so it meant, and still means in britain, any kind of grain with kernels. The Colonials naturally applied the word to maize when they came to the east coast of north america. For many years it was always referred to as "Indian corn", to distinguish from the corn (wheat, rye, barley) brought from europe.

Polenta is coarse ground corn meal. You can Google 'corn meal in England'. I doubt that corn meal really works, but I don't suppose it could hurt either. Is your pond cement lined or does it have a liner. How big is it?

The pond is lined and is 10ftx8. I read on this web site about the cornmeal fix.Will the koi be upset if I add it?

I suspect the Koi would find it delectable, but wouldn't it promptly clog the filter?

Order "polenta" in a European restaurant, and you will be brought a greasy, ghastly slab of a sort of fried cornbread.

I have not got a clue to be honest? It was a question in desperation.The other member did not say his was blocked.Looks like more research for me.

My mothers uncle, decades ago made a paste of cornmeal and wheat flour and used it for bait fishing for wild carp in a farm pond. Koi are supposed to be carp. I wouldn't be surprised if your koi tried to eat it.

How about we focus on the leak rather than the cornmeal. Yes, I see a couple of unconvincing and rare posts about cornmeal. Why do you even think you have a leak? Do you have plumbing for a waterfall or a drain or a filter? We have often been able to help with leak detection.

Carp make good catfish bait. I haven't tried Koi, though.

I have been ponding for many years and sorry but cornmeal will not fix a leak. Most leaks are found at waterfalls, filters and plumbing connections. If it is a liner issue you can patch it, but the surface of the liner must be made pristine for a patch to hold.