my guess its that its the 1 or the 2, but not the 2.5. i think its the 2.
i have the 2.5 and its got the printing on the tank. i saw a youtube from a while back and the atty heads were longer, the center tube was shorter. i think that would be the 1.
again, im not ultra helpful. im really surprised nobody has commented. i hate to say it, but posting in the general forum seems to get questions answered more quickly. its not the organized way and its not recommended because of how off-topic it can get in there. but the simple fact of the matter is that more people are in there and the chances of you getting an accurate response much much larger.