LOL! No pond has zero debris in it, but the trouble is if you use pool liner, you see EVERYTHING. There's a reason that a pond liner is black.
I have a backyard pool with a blue background, and every leaf, every twig, every fly that drops in can be seen VERY clearly. So, we get out out our pool vac, our net, and go through all the nonsense to get every speck. If my pond had a blue background I think I'd kill myself! LOL!
If you had a great filter, and a great pump you'd see a mongo difference. Trust me.
We need to get you up and running with a good situation to help you. I just think you selected a filter model that doesn't work. Gravel in a filter set up as you've got yours is just plumb bad. There are wonderful sand and gravel DIY filters that work like no one's business, because the sand acts as a fines filtration to get rid of all that little suspended crap you are seeing. They are not easy to clean and require an air blower to blow all the gunk outta the gravel. The blower is not cheap either, it costs $250. But when you blow out the thing weekly, you do end up with water that is like polished glass.
Your filter design is sort of like that one, but lacks the sand and the blower. So, you're in a no win situation with it. If you were willing to replumb that very barrel, we could help you do it.