Welcome to the forum if this is your first posting.

Very nice layout. Your choice for water flow is borderline for a falls that high. Refer to the pump flow chart either in the directions or on the Manufacturer's website. Figure every 10 feet of hose equals 1 foot of elevation when you begin to determine how much water is actually flowing out of the falls. Always use the next size hose for better flow. Always better to think there is too much than to think, "Oh I should have gotten the bigger pump". You can always divert the flow. Elbows also decrease efficiency.

For a really nice display go for a 2x capacity even 3x. It is all a matter of taste and what effect you are trying to achieve. You can trip the water rushing down the falls with a bowling ball boulder at the bottom or force the turbulance down to the bottom of the pond to keep the layers of the water column moving and mixing. Add more rocks on the falls to change the tones.

You'll have massive air exchange on the falls. The water will release CO2, and gain O2, thus helping keep a balance. That's a good thing for a well planted pond and any pond for that matter.

-Philip

Thank you Phillip!! My fiance has been saying get a smaller pump you'll put too much O2 in. But I want the louder noise so I'll follow your advice ;) Hopefully I can drown out the neighbors next door!
Thanks
Lena

Go to the Dollar Store and get another fiance. OR Ask his Mom if there is a warrantee. Kidding. Tell him you appreciate his input, thank you, and that falls need a high flow rate for a magnificent display. Size counts (sorry). Patch up his ego by asking for his manly help with the plumbing. Ice cream is good here, too. Plant some creepers along the falls for contrast.

Like communication, teamwork is very good. Good that you 2 are planning together.

You can pressurize a closed container of water with an O2 canister, and you cannot super saturate an open body of water. The air exchange at the falls will help stabilize the PH just by releasing the CO2 which will bring down the PH. So why are there so many falls in the wild?

In the daylight we all know that plants use CO2 and exhale primarily O2. At night in their dark phase or respiration phase, they are using the same O2 that your fish and the bio filter need to survive. So when a hot day comes along all of this is compounded. Your pond can be viewed like a living organism, all of its components are vital to its survival.

It's your project, do it your way.

I'm agreeing with the above posts, but thought a bit was missing: If the bottom of the pond is 4' below the lip of the falls, then the pump only has to lift the water 2' (the lift height is from water surface to waterfall lip). With a fairly small UV, and assuming the entire pump capacity is going through the UV, then you may wish to stay with a modestly sized pump around 1000 gph. Faster flow will reduce the effectiveness of the UV, and 800-1000 gph will provide appropriate circulation for a 500 gallon pond. However, you can use a larger pump and split the water flow so only part goes through the UV. The size and flow rate of the falls is personal preference. No worries about too much oxygen / air exchange. As mentioned above, bigger hose or pipes is almost always a good thing. The outlet size on the pump is typically smaller than the appropriate size pipe.