A couple of trichlor pucks in a floater should hold your Cl okay until you get back. To be on the safe side, I would shock it the night before you leave, then leave a couple of pucks in the floater while you're gone, then shock it again when you get home. If you just use 2-3 pucks, your CYA won't change drastically. Your pH will lower some, though--so I would up the pH to around 7.8 using Borax ( I would start with about 1/4 box in your size pool and go from there). It's not a huge deal to let it get a little high, since it's easily lowered with acid, but if you let it get too low (7.0 or lower), it can start eating away at your liner.

Janet