I've used the Seachem pH and ALK
kit and it is good. Right now I use the Salifert ALK
kit and the Salifert Ca
kit. The calcium kit is very easy to use and read and seems accurate, also a good price.
Unless you are testing for alkalinity, I wouldn't use a buffer to raise the pH. A pH of 8.1 isn't too low, when are you testing in your lighting cycle? pH will be lowest before your lights come on and highest right before your lights go out. Another thing to consider with low pH is gas exchange. If your tank is covered and there is little surface agitation then CO2
can build up in your tank and drive the pH down. Also, if the tank is in a room that gets little fresh air CO2
can also be the problem. To test this, measure the pH of the tank and take a sample out of the tank and put it somewhere where it will come into contact with fresh air, like near a window. Test the pH of the sample an hour or so later and if it rises substantially then you've got a CO2
problem. Aiming a powerhead at the surface, running a skimmer or even leaving a window open nearby can often help.