with your data, Chl a is 0.24 % DW, it is a little bit low, acetone is not the best solvant to extract chl a with cyanobacteria, try ethanol, see Ritchie 2006 and 2008.
If you need this paper send me your mail id at [email protected] I will send you this paper. actually, this is a nice protocol for chlorophyll extraction and estimation of chlorophyll.