Having a turtle pond is a lot different that just a Koi pond. We started out with just Koi, and then got turtles later on, but kept the Koi. Eventually we had to get rid of the Koi, as the turtles kept nipping at them and I felt bad for them. A full grown turtle can eliminate waste that is the size of a medium size dog, and sometimes if I saw it I would scoop it out. We also had frogs, and they would eat the tadpoles as soon as they hatched. The smaller turtles would eat the frog eggs, but some would escape and would grow to become frogs...not many made it. I had a small land area which was planted too, and there was a lot of maintenance involved with weeds, and they would destrop all the flowers, and it was also hard to keep any water plants as the turtles ate all of them. I don't know anything about the filters as my son took care of that, but I do know they were biological filters. It was beautiful in the beginning of the Summer with all the flowers and plants. We also had a smaller pond in the back of the yard for the baby turtles. It was fun, but a lot of work, and that's why I made it into a box turtle garden. Still work, but a lot less. Post some pictures of your turtles.