TBH.. your tank is still too young for that amount of corals especially SPS.. be mentally prepared for casualties..
0.3 drop of DKH in 6-7 days is nothing.. in fact your corals is not consuming any alk which means it is not growing and may have a chance not to survive...
We have the same tank RSR170.. i was doing 100ml ALK and 40ml Cal per day till i change to Calcium Reactor last week.. cannot tahan to buy RSF A/B/C..
BTW.. PH do not stay stable throughout the day... it goes up and down..