Hi bro,
I'm no expert myself, but allow me to make some comments.
I think the AL60 chiller may be a little under-powered for a 60L tank. Monitor how frequently it is kicking in and how long it runs each time. then compare with others to see if your chiller running time is acceptable.
The Green Algae growth seems a sign that your tank is cycling. (Even though you are using live sand and rocks) You made a wise decision not to add livestock immediately. You saved a fish from unnecessary stress. Good for you!
The white looking ants are probably Copepods, which are good.
Adjust the skimmer height and bubble size to get foam instead of water in the cup.
Barring inaccuracies of the digital temp reader inside the tank and chiller's thermocouple. The digital temp reader is reading the temp of water inside the tank, but your chiller is reading the temp inside your chiller. So it will never be the same. If you can, do an external temp probe so that the chiller measures the water temp of your tank.
Happy reefing