If the water is grayish and has a swampy odor you are having a bacterial bloom. Your bacterial culture in the used filter probably experienced a die back and will need to regrow enough to catch up with your bioload. I would recommend not fiddling with it very much, just keep doing 25-30% waterchanges every couple days and if you can get some add a couple tbs of filter sludge from a healthy filter to your filter pads. It takes a little longer to clear up a tank than it does to cycle in a new one but it should clear in a week or so Make sure not to over feed and as long as your fish are not starving now I would only feed every other day until the tank clears.

