Hi. I am new to this forum and could really appreciate some help. We have built a pond in our backyard that we started out using as a swimming hole. We had problems keeping the pond Clean and Free of bugs and algae and whatever else that's gross. We decided to get koi fish and goldfish to put in our pond and just turn it into a fish pond. The problem that we have is, no matter what kind of filter system we get and no matter what we put in our pond, it's always a dark green color and it's never clear and you can't see inside of the pond because the water is so gross. We have a liner on the bottom of the pond and once a year we have to drain the pond and pressure wash all the fun out of it and put fresh water in so that it can stay clear for about a month and then it goes nasty again. Our pond is 4 ft deep and 30 ft round. This is a pretty big pond and not your average backyard pond. We can't seem to find anything that is strong enough to filter out all the nasty inside of the pond and I want to make the environment for the fish very good. I want people to go outside and see the fish swimming around and living their best life but all I see is murky dark green water that looks disgusting and you would never want to get in it. We also have acquired some frogs who have found their way to our Pond somehow and I would like for it to be prayer for them to. Does anyone have any idea of what we could do to help keep our pond water clear and help our pond look really nice and clean? We have searched all of YouTube and we have talked to so many people and everything everyone has suggested has not worked. We even bought a really expensive filtration system and it didn't work either. The pond filter just kept getting clogged up with the nasty crap from the pond. Again, does anyone have any ideas that might be helpful? I'm at my wit's end.
Look into doing partial (10 to 30%) water changes on a monthly basis (or every two weeks) along with adding charcoal filtration. You may have more fish (& live critters) waste than you and your pond can deal with. Your water is accumulating nutrients which is causing algae blooms. That's where the dark green color is coming from...very small algae floating in the water. These algae specs are usually too small to see with the eye, but once there are enough of them the water will take on their color.
What you were originally trying to do (swimming pond) is very difficult unless you treat it as a swimming pool. That may include treating it with pool chemicals and having a filter system big enough for the total gallons of the pond, this means no fish (or critters). Maintaining a back yard pond (not pool) should be less effort, but the live critters will complicate things. The more fish, the harder it gets. Regular ponds like to have water throughput, for refreshing the water, hence my suggestion for the water changes. Charcoal filtration will compensate for less water exchange by removing the ammonia (fish waste) from the water and a good bio-filter should help remove some of the nutrients that your algae blooms are utilizing. Dying the water will also help reduce the blooms, but you will still be fighting the nutrient build-up and adding a different "darkness" to the water.
With a backyard pond, you have to think of it as an aquarium and pay regular attention to the water chemistry and try to keep it away from the levels that pond algae and pond scums thrive in.
A clear pond is not a healthy pond for aquatic species. If you can see more than 3 feet, the water is somewhat sterile. If you want a relatively sterile pond you can swim in, with a significant reduction in algae and some insects but safe for fish, humans and the environment, I suggest sodium carbonate peroxyhydrate.
However, if you are draining, cleaning and refilling your pond annually and still have these issues, you have major runoff into your pond. Your issue lies outside your pond and not in it. You have to fix that, first. Post a photo of your pond, and when I write, your pond, I mean the 50 feet of ground around your pond.