Definitely get a skimmer. It can be done without one but, requires an increase in water changes and more discipline on the aquarist part. I would run a skimmer and a sump refuge with cheato. Also, the skimmer isn't the place to cut corners. Get a quality skimmer and one rated at minimum of your system capacity to double of what your system capacity. As a couple others have said, your could try an algea scrubber, but I still wouldn't go without a skimmer. Best of luck with your setup. Being you recieved it from another used. Clean the tank and all the equipment thoroughly. I would fill the tank up with tap water, dump about 4 gallons of plain white vinegar in it and put all your pumps, powerhead and anything else you can hook up to run water through for 24 hours, drain and fill back up with tap water again for another 24 hours to clean it all out. Any coralline and and scum built up will rub right off within the first 24 hours. It works and I have used this method, plus it is completely safe.