It appears you are loosing anywhere between 0.3-0.6 ppm per day of Alk. Its time either use Kalk for all evaporated water or 2 part dose, or eventually both. Choose your method, and go for it.
I manually top off about a gallon at night. Will this effect pH or cause huge swings.
i\If you top off with Kalk yes, but only temporarily, nothing to worry about.
what are your nitrates at ? I would invest in a ATO it is much better then doing manually .You may be shocking the system by adding Kalk and RO at one time . What Is your SG at w before you add the RO water ?
I also have a 60 gal tank ,why are you losing so much water ? my ATO hold 3 gals and I fill it every 3 or 4 days .
I only have the fans running during the day when lights are on then half hour after dark . if you do that it might help reduce evaporation
For those looking into silent yet efficient fans... google silenx fans. That is what i use, Try finding a fan that does 90 cfm at 18 dda. 90 being cubic feet per minute, dba meaning sound. I challenge you.....
Changing that alone will make a world of difference if your using cheap computer fans.
It's not a computer fan. I found a clip fan, probably about 8" circumference. It dropped my tank temps enough that I need to run a heater. It's fairly quiet. You hear the overflow over the fan.