The pulsing of the pump is the nano osmolators equivalent of an alarm and happens after the time out is reached. By default the time out is 1.8 minutes but that can be extended to 3 minutes.
Is this the 20G in your current tank info? If so I would check if the float has any tilt, is it straight up and down or is it tilted toward the magnet holder? If it is tilted that means the magnet holder is pulling it and is the issue. This can happen on tanks with fairly thin glass and usually all that is needed is a pad between the outer magnet and the glass, a 1/8" sheet of acrylic or a piece of cork or rubber, even an old mouse pad cut to fit should do the trick. The black ring in the float is a magnet and it actuates a switch inside the post, any magnets near by and this can also include a ballast or LED driver or magnet cleaner can effect it. The magnet holder itself can be an issue if the glass is thin because the strength of the magnet is too high and attracts the float, we tend to see this most on 1/8" glass.
