Biology experiment with algae method help
For growth you could measure the mass of algae before and after the experiment. If you have a centrifuge you can pellet the cells or use a filter to remove the culture medium. Alternatively, if you have access to a hemocytometer and a microscope, you could get an accurate cell count that way.

For controlling pH, you'll need a buffer in your culture medium. You should select a buffer with a pKa close to the pH you want to test and then titrate the pH of the medium with a strong acid or base (HCl or NaOH). Make sure to check the pH before and after the experiment to be sure that it didn't change due to growth of the algae.