Your plans for a pond sound good. Definitely make the drop deep from the edge. Shelves, particularly the many level stair-step kind, not only provide easy access for predators to utilize when entering your pond, but also alter the usual formula for estimating water volume. .

A UV is great for elminating green water, but low stocking levels of fish and good filters should accomplish that as well. Some people use bog filters and veggie filters, which compete with the algae for nutrients. A word on algae, though. Every pond gets a bit of carpet algae on the bottom and the walls. This is normal and healthy.

If you can, install a couple of bottom drains. That is one thing I did not do that I really wish I had.

I don't get a lot of algae in my 1000 gallon pond mostly because it is shaded. What little does grow is controlled by a small UV. I also have an adequate filtration system with lots of quilt batting. Since a pond is not a static construction, circumstances that control water quality are constantly in flux. Many new ponders are unaware that change is normal.

The trick is to not allow harmful conditions to get out of hand. That is why many old hands seem to test and fiddle so much. I have not needed to add chemicals to my pond in almost two years because I have been able to keep the basics under control. I do keep in mind that bad changes are always possible. The worst are often caused by contamination by storms, parasites, over feeding and overcrowding. I suspect that I will need to adjust buffering soon because of the heavy snow fall this winter. I intend to cut down some scrubby trees this spring so I can expect an increase in algae growth. I may be able to have water lilies and lotus if I can get around to installing a small side pond connected to the main pond in a way that doesn't allow the koi to destroy them. As I said, the pond is always in flux so circumstances change.

I have found that keeping oxygen content high is the best way to keep the pond healthy. Waterfalls and bubblers along with adequate filtration does that very well.

Once established, a large pond is usually easier to maintain than a small one because changes are smaller in affect and with a good maintenance schedule won't get out of hand.

Remember that no two ponds are the same just as no two ponders are the same.

Thanks for mentioning the quilt batting. I forgot all about that, and that is a regular maintenace item at my pond. Wrapped around the skimmer mat, it does a wonderful job of straining out suspended algae.

Will you have a waterfall? Do put in a couple of bottom drains. The sharp drop off is good for raccoons, but the herons will still find the fish if there is a good perch on the bank.

Lindyip,

I build a lot of koi ponds and I will share with you what I have learned over the last twenty years. First with your concern about Herons. Keeping the fish safe from heron is something that can't be guaranteed. But with the right design the risk can be cut down. A deep drop from the edge of the pond is the first step. It has to be at least 2 ft down to the first flat area. Deeper is better and I prefer at least 3 ft. But this is just the first step. The next thing that needs to be addressed is the pond edging. The last thing you want around the pond is flat surfaces that the heron can stand on. The heron will just stand on the edge and wait for fish to come by. I prefer to use round rocks that start in the water 8 to 10" under the water and protrude out of the water and over the edge. I have built koi ponds less then a mile from heron rookeries with no problems. My own koi pond I know gets visited by heron but I have never lost a fish in it to a heron yet my smaller garden pond a 100 ft away the heron get the fish all the time. The koi pond has been there for the 19 years.
Next I would suggest a bare liner with at least two bottom drains. The last thing you want to have to do is to empty the pond to clean it. Not because of the work involved but because it will destroy the bacteria that it take a very long time to grow. As far as a UV light it will depend on how patience you are. For the first few years you will have problems with green water and string algae but after about four years the pond will take care of itself as far as algae goes. That is how long it takes to grow the bacteria that will take care of the algae. But those first few years the pond can be out of control.
Mike