I'm a bit late to the party but I'll go ahead and throw out some additional conformation for you on your forward plan as well as some suggestions for moving forward. I too have an "Aquascape style" pond, although I used none of their products or published designs. It is simply the same mindset/concept of a self contained ecosystem.
Like other people have already commented these companies are out to establish money flow after the installment of the pond through maintenance service and product sales. I can tell you that in 3 years I have never once added any chemicals or salt to this pond, with the exception of when I had a parasite issue early on and had to do a medical treatment. With the exception of the first month of the pond being installed I have enjoyed crystal clean water with no UV, no mechanical filtration, no bottom drain pump, no chemicals, and little maintenance. And this pond holds 25ish goldfish, a dojo loach, several white cloud mountain minnows, and in the summer I introduce various freshwater tropical fish.
I owe this low maintenance to my large bog filter that can be seen in the foreground of my waterfall. Additionally, what cannot be seen in this image is the numerous underwater oxygenating plants and water grasses within the pond, which has a rocked bottom by the way.
With all this being said I do get string algae blooms every year. But a few days of not feeding the fish and some occasional physical removal of the algae typically solves the issue.
As others have said I could not enjoy this water feature if it were a koi swimming pool, which is what your koi expert is referring too. I have nothing against such water features, and have seen dozens of beautiful ponds constructed in this manner, including several built by members of this site. However, my personal preferences led me to construct an ecosystem more so than a koi aquarium.
Hopefully, that helps to instill some additional confidence in your path forward and helps you choose exactly what you want out of your beautiful pond. With all that being said my humble suggestions for your situation are as follows, assuming you wish to continue with the self containing ecosystem route.
-Plant in your bog ASAP!!! This is your ponds filter and its beating heart. You will be amazed how quickly the plants fill out and grow off the nutrients you will be providing them. Once you get the bog established everything else will fall into place.
- KOI LOVE TO EAT! This was one of the reasons I opted out of placing koi in my pond. I am a gardener at heart and love the plants almost as much as the fish. From what I have been told the majority of koi will rout around in the gravel bottom searching for pond dwelling critters and algae. Thus using oxygenating plants and pond grasses will be difficult if not impossible, especially once the koi grow to larger sizes. This leaves you with 2 options;
#1: Determine if koi are what you wish the pond to be built around. There is still time to opt out of Koi and go with goldfish instead. However, with the size and depth of your pond and from some of the comments listed I feel as though this is not an option for you as Koi was the entire reason the pond was built. This leads you to the next option.
#2 Create plant shelves where the koi cannot access the various water plants to get extra filtration. This will also provide safe havens for other pond organisms that serve beneficial roles in the pond.
-Leave the rocks alone in the bottom of the pond and allow the necessary micro organisms to colonize in those spaces.
-I would also go ahead and add the discussed bottom drain/pump, plumbed within the current system up to an additional bog area. From the pictures that have been provided it looks as though the current bog is not big enough to sustain that size of pond, especially with koi in it, which have a much higher load than other pond fish. Adding an additional bog will only further stabilize the pond and reduce overall maintenance on the pond.
-Return the chemicals and additives that you purchased if able. If not able to return, put them on a shelf in case they are ever required, but I would resist adding them.
FINALLY, HAVE FUN!!! This is your water feature and it needs to be designed to your liking. Neither myself or anybody else on this forum can tell you how to fully accomplish that. However, we can provided suggestions, and a helping hand when needed. As well as boost confidence. We have all been in those new pond owner shoes, I personally still feel as though I am there at times.
Good luck and I hope to see many future pictures of your beautiful pond in the future.
