You can get the quilt stuff from places like Dunelm Mill or anywhere that sells upholstery material, an actual quilt would also do of course, an old one would be fine. It's available in different weights..thickness..and could be useful...about £3/ running metre x 1" thick.
Maybe if you sweep the settled dusty stuff around, the quilt/waterfall/filter will catch the bits and get more of the sediment out. Failing that, it's a complete wash out and refill if you need to get rid of it all. I don't think the stuff that's settled out would get pulled through the filter or anything without any water movement as such as there's nothing to stir it up.
How deep is it at it max depth, just curious? The shallower the pond, the faster it will heat up and chill down, so the less stable they are making fish conditions trickier.
The waterfall doesn't seem to do a great deal, they're usually there to give both sound and aeration. The water as it's currently set up just seems to run along the rocks, not giving much of a splashing effect if at all.
It looks a bit better than in the previous pics.....but I can still see some issues, the way the filter is buried so deep, yes, they can go down to the point where the inlets are, but this appears to be buried below the lid line in parts, so it is too deep set, in my eye anyway.
You will have probs in setting plants on the ledges if you chose to do that as the final edge one is so shallow. The idea is to set them in pots on the ledge to make it look natural and disguise the edging for your natural look which I read is what you intended. However, setting pots on your ledge, the actual pots will stand up above the water and be seen from all angles.
The liner is also wrinkly and sticking up above the water level in some areas, these maybe places that it could get damaged.
I also think the run off will be a problem in heavy rain as soil could wash into the water, it doesn't seem to have been addressed.
I'm sorry that our posts seem to be so negative, we're really just trying to help. If as pointed out, you are entirely satisfied with the result you have, then that's good, but as you can see the majority of us here can see you have been short changed so to speak. Greenfingers are as you say a national company that one of my own girls uses. However, I'm not so sure that this team are experienced pond designers and installers, others may well be. It would be interesting and informative if you could get the thoughts of a truly good pond team to take a look at your pond and give you their opinion, either in person or by sending them the photos and just see what they say. Maybe it's worth doing....I certainly would. Please do keep in touch with us, and I/we hope that some of the issues we all seem to be pointing out can get resolved without too many extra £££££'s being spent