I was wondering if an xp2 is OK for a 55 gallon tank because I don't have the money for an xp3. I can get an xp2 on ebay for around 60 bucks but an xp3 is around 120.
I guess you could go with the xp2 for now, it's rated for tanks up to 75 gals and you probably have a little bit more than half of that in your 55 gal. You could always buy a second xp2 whenever you have the money. That's my 2 cents.