Well, it could be a couple of things from what you've told us. First (hopefully) the substrate; I say hopefully because if this is the source it will clear without trouble. I asked about the filter because that should help it to clear.
Second, could be a bacteria bloom, common in new setups. This will also clear on its own. This I would think should be white though, so probably not pertinent here. Water changes would make this worse, or at any rate it would not clear as quickly as leave it alone.
But more likely, Third, if it is really more green than brown then it is likely "green water" which is an algae bloom that occurs when light and nutrients exceed what the plants can use. And without fish CO2 will be minimal so the plants are held back by that shortage [the law of minimum I've mentioned elsewhere], this nutrient carbon is not included in root ferts. Working on the assumption this is the cause, reduce the light. You have swords, so 8-10 hours a day light on, use a timer to be consistent; and a couple water changes. These will help clear up green water provided the light is reduced as well. Cut the light back gradually, e.g. if it is on for 12 hours now, reduce it to 10 for a week or two; if that doesn't do it, reduce it another hour. Rather than all at once.