Hi,
Further to Steve's comments, it should be understood that CO2 concentration levels do not necessarily track with tank water pH. This is one of the major difficulties with a pH controller. pH stability most often comes with the penalty of CO2 instability, which can both induce some forms of algae and cause toxicity.
Until you gain a better understanding of your tanks profile it would be better to de-couple the controller and to simply use a constant injection rate. The injection should be timed to turn an hour or two before lights on and to turn off a few hours before lights off. You can also use a dropchecker to get an idea of the CO2 levels.
Algae due to CO2 related issues are specific however, so just to make sure, as Steve mentions we should confirm what kind of algae you have as well as more details of the tank, filtration, lighting etc.
Cheers,