The males can get upwards of 6" SL. They aren't terribly picky for a blackwater species of ancistrus, but you have to keep in mind that high pH like we have around here makes ammonia far more toxic, so more of a risk. They seem to prefer 78-82 degrees.
Just worth mentioning incase you weren't aware, but you need to let tap water settle for approximately 24 hours (with some aeration) before you will get a true pH reading.