Big Temp Drop - Help!

[chophousemusic]

So im in the process of my fish-in cylce. I have 2 zebra danios, 2 buenos aires tetras, 1 blk phantom tetra, 2 silver dollars, and 2 krib cichlids. a 75 gal tank with 120w stealth heater. I did a water change last night and unfortunately my hot water and heat was out in my house cause my oil tank needed to be filled. So i used a combination of cold water and warm water that i boiled. Since it was only a 20% water change the temp dropped from 78 to 74 degrees. So i turn the heater up before I go to sleep to almost 80. I wake up this morning...my house temp is at 50 degrees and the tank has dropped to 70 degrees. Since then Ive gotten the oil tank fixed and house is in the process of warming back up. Is it becuase the temp in my house dropped that the tank dropped cause that usually is not the case in my house?? And how low can the the temp go without harming the fish ?? What is the best temp to keep these fish at ??

 

[WILDER]

Temp depends on which fish you keep.
Just search the fish you keep and see the tank temp for them.
If temp gradually dropped the fish should be ok.

When preforming a water change shouldn't alter temp more than 2 degree's each way.
Don't do warm water changes. Just let the temp go up gradually.
Let temp go up gradually, don't do warm water changes or alter heater temp.