I'm starting to purchase equipment for my new build and I'm having a hard time choosing a skimmer. My entire setup will be about 130 gallons with the sump, but after rock and sand displacement probably 90-100 gallons total. Do I look for a skimmer rated twice the amount of water that's actually in there or 130 amount? My ultimate goal is only having to do a water change once a month. Thank you for any help