you can use phenol red which is a pH indicator and will turn purple at a pH of 8.0+ and it will turn red at 7.5 and yellow at 7.0- ..so if you figure you can get the color from an 8.0 (count the amount of substance it takes to lower the pH) to a 7.0 and if you get the hang of it, you can get pretty precise (at least I can - I measured myself with the phenol red, eyeballing a 6.2 and we confirmed with a digital reading). this is just my
.. I usually recommend a digital pH reader, but nothin' cheap.