I don't understand what you have against bottom drains and bare liner ponds. Enough with the whole balance of nature and ecosystem in harmony stuff. Rubber liner isn't natural, that's why you use gravel and I use bottom drains! There are biofilters out there that take care of the break down of fish waste and other bad bacteria.
I have stated no less than 3 times in this thread that bottom drains can be appropriate.
The disregard of "balance of nature and ecosystem in harmony stuff" is exactly why the problem of pollution has reached a critical point. It won't cause pollution in this case, but it is that particular mind-set that troubles me.
As to a bottom drain not being beneficial to the fish, both Koi and Goldfish are by nature bottom feeders and if you remove their ability to act instinctively in feeding, a certain amount of stress is placed on the fish. No amount of stress is beneficial. Gravel provides the media to support this natural behavior.
I believe that rocks and gravel in a pond more closely approximates a natural habitat for the fish which, to me, is a value worth the extra maintenance
You are evidently of the school of whatever involves less maintenance is the path to follow.
Koi and Goldfish can be kept and enjoyed under both venues.
is an excellent site, as I stated earlier. Another excellent, and older, site is www.koivet.com
that is hosted by Dr. Erik Johnson DVM who has been a universally respected authority on Koi health for many years. He thinks gravel bottom ponds are fine, in fact he had a quite large one built for his personal use a couple of years ago. And yep, no bottom drains.
I will say it one more time: It boils down to a matter of personal choice by the customer.
I almost forgot, biofiltration does absolutely nothing to inhibit "bad bacteria", all it does is provide the basis conversion steps of the Nitrogen Cycle.