coolant loss on 2010 Civic LX

On February 24, the dealer checked all fluid levels, and, since then, I hav e noticed that the level of coolant in the reservoir was low, so I bought a
gallon of Honda coolant and added enough to bring up its level to just bel ow the upper mark on the reservoir.
I noticed that the Honda manual says to change coolant at the Service 5 lev el. My car presently has about 13,xxx miles on it. Can anyone say when th e Service 5 level comes due on a 2010 Honda LX because I'm not planning on taking my car in just for a low coolant level -- unless it's indicated to t ake it in for this.
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