Temp is no problem with adding lime. Buy a few bags of ag lime from your Co-op and add it as needed. But a pH of 6 does not necessarily mean you need lime as pH changes during the day/night. Alkalinity is the best thing to monitor. The new water plus the fact that hydrated lime wears off in a few weeks probably means you could use a little lime. I would suggest that since you added 2500 lbs (it takes a while to work fully) that you buy a couple bags and dissolve it into the water (rather than let it sink to the bottom. In your current situation treat the new water not the pond bottom dirt.