Can't get good alkalinity levels

Hi,

I´ve been fighting hair algae for a year. I tried everything, then i
found my KH was too low (4,5 dkh) and calcium too high (550).
I tried to put things right. So i stopped adding kalk and started
dosing Seachem's Reefbuilder.
I had to dose lots of this product to reach 8 dkh, but, when i stopped
dosing it just for one day, dkh fell around 1 or 2 dkh.
Then I realised calcium fell to 280, so i restarted dosing kalk
through my kalkwasser reactor.

Now calcium levels are fine at 420 and i still can't get my alkalinity
higher than 7,5 dkh. I stopped dosing Reefbuilder and i am now dosing
C-Balance:
30 ml part A daily
60 ml part B daily (I want to get my alkalinity to 10 dkh and mantain
my calcium levels)

I have tried water changes and didn't solve the problem. KH isn't
getting higher.

By the way, i have a Deltec Fluidised Calcium Reactor (PF600). It's
outputs a 40 dkh and a ph lower than 7,5. This calcium reactor
doesn't seem to help

Hair algae persists. What should i do? Add more part B of C-Balance?

My tank is 180 gallon with mixed SPS and soft corals. 4 small fish.
DSB and lots of live rock.
Some coraline algae grows behind the rocks.
I have a huge efficient skimmer (Aqua-Medic Turboflotor 5000 Multi).

Than you for your help,

Reefman