....On a note, my PH is always low ( 7.7). I dose alk to bring it up (but making sure its not too high) and i drip kalk at night to help with PH too. But it didn't seem to be working.
To add a little perspective - I have two large systems that I look after with carbon dosing: one total about 500g using biopellets; and the other approx. 1000g total using EtOH/vodka.
The bp system struggles to maintain a pH of 7.9 - 8.0 and I do have cyanobacteria in this system. On this system, the only form of aeration is from a relatively small protein skimmer (only 6" diameter by about 18" high); the primary circulation (not including powerheads) is just enough to turn the tank volume over about 2.5x per hour, however, thanks to the bp: NO3 is 0 and PO4 is 0.28. On this system, even when I pushed the alk up to 12, the best pH I was able to achieve was about 8.1 during the photoperiod...
Alternatively, the vodka dosing system just happens to have quite a large oxygen infusion regime. It has two large beckett run Protein skimmers (each are 10" dia by 48" high; plus a ginormous bio-tower (18"x24"x42"H); plus 2 large macro algae refugiums on reverse photoperiods. On this system, Nitrates are also around 0ppm; and PO4 hovers around 0.32... there was a short bout with cyano on this system as well, but eventually ran its course after about 3 weeks away from iodine and a focus on elevating pH. Pertinent to this discussion is the fact that on this system, I've been able to achieve a pH of 8.1 - 8.2 with my hardness hovering between 6.5-7.5.
In other words the system with a good strong strategy of O2 replenishment, has a greater capacity for alkalinity without upsetting pH if that makes any sense.
Sheldon