Just buy new. I bought mine and don't regret it. I am usually the guy hunting for that used deal. Unfortunately when a used Apex comes up for sale, it's usually gone within a few hours. Get the full apex with a ph probe (one for ur calcium reactor, and one for your tank. Im assuming u already have one ph probe, u can use that one with ur apex). U might want to look into an extra EB8, that's the only upgrade u might want. Maybe just an eb4, if u only need a couple more plugs.