My tropical fish tank is 67 F is this OK for the fish?

I have never had a water heater since I live in Miami and the tank temp is always around 74-76 F but this week has been really cold and when I check the temp in the tank it says like 65-67 F in the morning. I have all tropical fish, neons, swordtails, gourami, angelfish, synodontis catfish, serpae tetra. Do you think they'll be fine for this week or do I urgently need to go buy a heater. Thanks for any help.