Your pH, although important, isn't a number you should be chasing, as long as your other param's are within acceptable ranges. Testing is another issue, most liquid, or test strip test kits don't have enough resolution to give you a truly accurate reading, so your readings may not be as low as you think they are. The closest you can get would be using a decent pH meter. i.e. Pinpoint, Apex, RK, etc., with a properly calibrated probe. The pH in your system is controlled primarily by the amount of CO2 in your system, and through gas exchange, surrounding household atmosphere, and will have a daily swing being lower in the am and higher pm, thereofore, its best to measure at the same time each day. A good gas exchange, via surface agitation, skimming, etc., will help the CO2 in your system reach equilibrium with its surrounding atmosphere. During the months that your house may be closed up, you will experience elevated levels of CO2 in the household atmosphere, which will tranfer to your system, having an effect on the pH. This is the reason running a separate outside air souce can be helpful.
Anytime you add an alk supplement, you will see a temporary change in your pH, but once your system reaches equilibrium with the surrounding atmospher(again the CO2 thing), it will return to its base level.
