Early pond building
When I built my own pond in my back yard in 1987, filters and skimmers were used on swimming pools, not ponds. Flexible rubber liner ponds had not yet been heard of. I used a PVC liner that was meant to be used as a liner in sanitary land fills. A pond pump was bright blue and normally used as a sump pump in leaky basements. Shortly after I started building ponds commercially, a few companies started building pumps especially for ponds, made them black and different sizes. We connected the pump to a garden hose to run water over a waterfall. If we wanted two streams of water over the falls, we used a hose divider to get those two streams. The largest pond pump was 1200 gallons per hour.
The pond market grows
Within a couple of years, companies realized that backyard ponds was the niche market of the future and started making products strictly for ponds. We had bigger pumps, special hoses, special dividers and now needed hose clamps. Our liner choice was still laminated PVC.
But the market grew and as it did, opportunists arrived. Until skimmers and filters were marketed, no one needed them. Koi pond enthusiasts were already using elaborate swimming pool filters. I was known to remark that the filtration system of a koi pond I was working on looked a bit like a heart - lung machine. If you wanted a pond with goldfish and plants, you did not need a filter, nor a skimmer. You still don't.
The new pond companies that were proliferating throughout the country began to convince pond installers and do it yourselfers that filtration was a necessity and no pond would work unless it had a skimmer.
Filters and skimmers arrive on the market
Pond filters and skimmers are relative newcomers to the pond building industry.
A pond skimmer is a black plastic box that attaches to the side of a pond with bolts and nuts through the now rubber flexible liner. The pump sits inside and draws pond water through the skimmer into a basket inside and removes surface debris before sending the water on over the waterfall. You clean the basket periodically.
If you build your pond under a tree, you might need a skimmer. Unfortunately leaves that fall from a tree don't stay on the surface very long and that skimmer cannot get leaves or other debris off the bottom of your pond. So there is your skimmer with the nuts and bolts and seal that have penetrated your liner. If the seal fails, and it frequently does, it can cause huge and possibly unrepairable problems.
A pond filter removes organic debris from your water, cleans it and returns it to your water. And it does a remarkably good job at that. If you feed your goldfish, you probably need a filter of some sort. I like the under $10.00 homemade ones. They do an excellent job.
Balance your pond
So how does your pond survive with no skimmer or filter? Balance it ecologically, with submerged vegetation and floating plants that cover at least 50-70% of the surface area. Do not overload your pond with fish and most importantly do not feed them! Those fish live off the submerged vegetation, usually anacharis, and the fish waste fertilizes it. Anacharis grows faster than the fish can eat it.
You don't need a pond filter or a pond skimmer. More money can be in your pocket to spend on better things than pond filters or skimmers.
Marketing works, but nature works better.