How much phytoplankton do you feed per day? Live or Instant Algae?
From my limited knowledge, you do not need light to culture rotifer unless you are using live phytoplankton. Just ensure that the water is slightly green at all times. Since you are keeping it at room temperature, did you do any water changes? The culture water is pretty dirty if you do not carry out water changes since the metabolism rate is high. It is recommended to harvest about 30% of the culture everyday to ensure optimum density and water quality.
It may be a typo but specific gravity of 1.17 is too high but 1.017 is fine