I have two turtles at home, I am pretty sure they are red ear Sliders. I got them in China town 5+ years ago, when I got them they were about the size of half dollars, very tiny and small. At the time I didnt know it was illegal for the people selling them to do so due to the fact the turtles were still babies.
Anyhow its 5 years+ later (dont remember exactly how long I have had them)
and they have lived and grown together.
I have a few questions about them, sometimes I see them nose to nose and one of them is patting (best as I can describe it) the others cheeks.
What exactly are they doing. Is this a mateing ritual? or are they just playing?

Also how big can they get. so far one of them is abut 10 to 11" (shell) the other is 7-8" (shell) they seem to get bigger every year. Will they stop growing?

Also what is a really good external canister filter to get, I am using a fluval 404 but it just doesnt seem to cut it. This may be because its 7 years old it has all new propeller and ceramic shaft ect. IT probably due to the fish tank not being filled up all the way.

Thanks guys.