slow growing pond plants?

Nice garden, Randy, you should post some more pics of it!! Thanks for the pics as they do give us a better idea of the situation.
First let me show you my wild life pond, which does have fish in it, just to show you I do have some working experience with them. The pond was dug around 1995 the water has always been crystal clear and includes a waterfall which is hidden in the undergrowth!



I think there are two major things that need to be done, if you're willing! First is to put a bit of oxygenating weed in there such as Ceratophyllum, Elodea, Largarosyphon. The last two are aggressive and will grow quickly using up the nutrients in the water and when it's clear you can keep them in check. I've planted a lot of marginal plants in baskets in the pond, such as Ranuculus, Yellow Flag Iris, Reedmaced, Veronica, Zantedeschia, Sagittaria, and they too are taking nutrients out of the water denying the algae of food to grow. I used small plastic baskets from Wilco's which resemble the washing basket. I filled the baskets with ordinary soil after laying hessian on the inside, put the plants in and covered the soil with gravel. What minimal nutrients that's in the soil will get used up almost immediately and the hessian takes years to rot by which time the soil is bound by the roots of the plant. That was 17 years ago and the baskets are still there with plants in as good as ever. Mine are on ledges built into the pond, but you can use bricks to raise the baskets up so that there is just two or three inches of water over the top of the basket. The more marginal plants you can get in the better.
Second is to discourage the ducks!!! Netting the pond looks to be the way to go initially, but making the net higher to all for the marginal plants should you want to plant some. I think you will have to put up a barrier of some sort, either living or a fence to keep them away once the net has given them the idea that they can't get into the water. I consider my wild life pond to be low maintenance as I only go in there around once a year with waders, as it's around 3' to 3' 10" deep, to tidy up and pull out any plants that have got to ambitious. A pond, just like a garden, is a very personal thing so advice can be given but you must decide what you want.

 

Well, the first[Marsilea Quadrifolia or Water Shamrock] is an aggressive grower and will suck up the nutrients quickly....it will also need taking out from down below when you need to keep it in check. The second [Ranuculus Aquatilis or Water Buttercup should do a good job of taking out the nutrients, but both the first two are marginals really and not oxygenators. The third [Pista Stratiotes] is a floater and not an oxygenator. It's also a tender plant and will not survive the Winter in the pond and, if you want to keep it, you have to bring it into a frost free area in a bowl of water. If you can find one of the oxygenators I mentioned it would help you greatly.
It is nice to have ducks coming into the garden along with other wild life.....but there's always a flip side!!