this is what i test for and recommend you do as well if you dont already, something is off?
trates
ph
alk
ca
phos
mag
if it isnt get your salt to 1.025 w/a refractometer not a hydrometer!
running a phos reactor is a good idea when 1st starting everything up, a fuge should take its place when the macroalgae starts growing like a weed!
My ph was a little low like yours and i started dosing limewater (Kalkwasser),
my main problem was my mag was low and was causing me issues w/ alk, ca & ph,without getting in too technical the amount of magnesium getting into calcium carbonate skeletons is related to how much magnesium is in the water, i would test for all of the above and if you dont have one already get a fuge going, you can dose small amounts of iron to give your macroalgae a kickstart, it should make your macroalgae grow like weeds!
I use kent tech m to dose mag, i have been using coralife salt and seems to run a little low on the mag...unless i got a bad 150 gallon bucket?.