I've never seen a hose "expand" before, on my pool, they just look like they "stiffen up" some with a bit of movement, but then they equalize and settle and look the same as always. I'm not familiar with the Chlorine pack you're describing since I only use bleach, so I really can't say whether that is part of the problem or not.
I wouldn't trust it not to pop off again, not something you want happening when you're not around, I would look into it a bit further because it just doesn't sound right.
Can you run without a chlorine pack and see if the problem goes away?
A chlorinator should not give that kind of backpressure to expand a hose.