IMO,the most important things to test for weekly are PH,alkalinity,and nitrate(NO3).Of course this is in a reef that is already established.When setting up a new reef,dont waste your money on ammonia,nitrite,phosphate kits.The first 2 will only need to be monitored during the initial phases of the cycle(anywhere frome days to weeks).These tests you can have done at most LFS for free.
When your tank is finished cycling,ammonia levels will drop to 0,then nitrite to 0,then nitrate levels will begin to rise.While your tank is still in its infancy,you wont have much of an alkalinity /calcium demand.You probably wont need to add any supplements,just do waterchanges to keep NO3 levels down while waiting for your tank to mature.
Alot of tanks experience an algae cycle as well,dont be alarmed this is good.Remember,algae remove NO3 and other nutrients from the water.The first algae to come is a brownish film on the glass/LR,these are Diatoms.This is usually a good time to add snails(as long as tank is cycled) as they will eat them.Green hair like algae is usally next to take root if water conditions aren't that good(high PO4,nutrients,etc..)Snails and various herbivores will eat this but water quality is the most important thing to keeping it from growing.Last,will be pink/purple calcareous algae known as coralline.This algae is desired by many because of its color,and its encrusting nature.This algae uses alk/calc as it grows and when it starts,you will notice an alkalinity depletion when you test.This depletion needs to be replaced with a balanced calc/alk supplement.
One of the biggest mistakes newbies make is buying alot of snails/hermits to control the algae.I feel these should be added gradually at the rate of the algae growth in the system.For a 75 gal,20 astreas,20ceriths,and 20 nassarius snails would be a good start.Of course only adding 5 or 10 of each at a time.I dont like hermits but many use them as well as an algae cleanup crew
Corals are also a big part of the nutrient cycling in tanks.Once things get stable,dont be afraid to stock your tank up with them.They do a wonderful job at uptaking nutrients out of the water leaving you with higher water quality.
The best thing i ever did with one of my reefs,was allow it to mature for 4-5 months before adding lots of corals/fish.By not having any predators in the tank,it allows the fauna(pods,worms,etc..) in the tank to populate which in turn will increase the tanks nutrient processing/stability.