1stly - I would add about another 10kg/25lbs & also increase your flow rate
Your flow rate is also quite low - 2 x XP3 only turn out 700 gallons per hour (GPH) - which means your water is only being turned over 9 times per hour
This value should be around the 20x or 1600 GPH, this is very important to maintain the bacteria that colonise on your Live Rock
If for example you added a
M1100/4400 lph Seio Superflow Pump Aimed at your surface this would :
A - Give you good gas exchange & introduce Oxygen in to your tank
B - Increase your overall flow rate to 23 x the tank volume
C - It will remove any scum from the surface
What Skimmer you using
What is your Tank readings - Ammonia, NitrIte, NitrAte, Specific Gravity,pH
You temp aint that bad, If you are having problems maintaining a decent temp then you may have to look into addin a chiller or a fan.