Could be from the substrate. Is that flourite mixed in there? Not a big deal either way. Many tanks will cloud the first few days or so. As mentioned, a few water changes will help. I just wait these things out at first. Things will get uglier before they get better. You'll most likely deal with all sorts of funk during the first couple months between algae, fungus from wood, bacteria, decaying plant matter, etc. I personally don't start to do water changes until nitrates get around 40-50 ppm and test show no traces of ammonia and nitrites. It really doesn't matter much either way, as the bacteria you want are colonizing all over everything in your tank anyways, not the water itself. I just like to keep ammonia levels consistent and water changes cause unnecessary work, IME.
Have you looked into doing a fishless cycle? I recommend it for the sake of the fish. Some use "starter" fish with the use of seachem prime. It works, I have even done this myself but try to avoid it whenever possible. Much faster cycling time with fishless, though.