Hi there,
I recently purchased a 55 gallon tank for my approximately 2.5 turtle, so along with the tank upgrade, came following the filter. I purchased a used Fluval 404 unit, and tested to make sure that the intake was working, and that it was spitting out water properly. It was, though as soon as I used it, I noticed the water was starting to get a little murky. I figured it was because the filter media was so old (as I had purchased from an individual who hadn't used it for about a year), and about a week later, got some new media.
I thoroughly cleaned the inside of all the tubing, purchased brand new foam, bio-max media, and charcoal, and even installed a surface skimmer. After doing a water change, the water appeared crystal clear for several days. But now it's back to being murky.
There's practically nothing in the tank, and no other fish other than a tiny algae eater. I feed my turtle outside of his tank everytime in a feeding container... so there's really nothing else that's hitting the water. I do use algae/water conditioner when I do my partial water changes as well.
Any ideas?

