Cold tank

[Myka]

I know my response is too late to be of any help...

18C or 64F is very cold. If temperatures stay above 70F there isn't usually any trouble. Even though the temperature wasn't that cold for that long, I would still be very concerned. I would be trying to warm the tank up to 70F as quickly as possible.

If there is mature macroalgae in the tank even relatively small temperature swings (both down and up) will often trigger a sexual response. Be ready to do some big waterchanges if that's the case.