Keeping a pond healthy and happy is a labor of love. An imporperly designed pond (like your sounds like it is) can be a real maintenance nightmare. A pond should have excellent filtration, clear water and no sludge or debris at the bottom. Also, it should have no more than 1 koi per 250 gallons or 1 goldfish per 50 gallons. Your pond has approximatly 1200 gallons if it is recangular, much less if it's round or oval and also depending on how much of the pond is 2' deep and how much is 5' deep. but lets assume it has 1200 gallons. That means you have room for 24 goldfish or 5 koi, IF you have good filtration. but you have none at all, so your pond is a problem waiting to happen. It can't go on like that forever. Parasites and harmful bacteria are breeding in that sludge and could sicken or kill the fish. Hudrogen sulphide gas can also form in that sludge and kill the whole pond.

So if you want to keep it....you need to get some filtration installed. Get a water test kit and check the water. Get the pond cleaned of all debris and sludge. this needs to be done now, before cold weather sets in because if the fish head into spring in a filthy pond, they are sitting ducks for massive parasite and bacterial infections. And find new homes for most of the fish....only keep a very light load for yourself. Like I said....koi keeping is a labor of love. Try it for a while. If you don't enjoy the upkeep, then fill it in, or make it shallower and stock it with plants and forget about fish....just make it a nice shallow water garden. that would be safer for the kids anyway.

I am having a large pond built right now and probably near you. Would you like to rehome some fish? Maybe talk to my contractor about the cost involved in getting the necessary filtration installed?

By the way, I have two kids ages 5 and 8. I understand your concerns. I waited to build this pond for many years. Until my kids "listened and respected my safety rules" and learned to swim. My pond is being built with children in mind so that they can explore it and play in the river and use stepping stones to cross it.