Conversion from Bacquil to chlorine

[Quaker]

I am starting the process of converting from bacquil to chlorine. My pool water is very green. Should I
put in algecide first or change sand in filter?

[chem geek]

You change your filter sand at the end, not at the beginning. I wouldn't worry about the algae at this stage -- you'll get rid of that in the process of adding chlorine to convert from Baquacil, assuming you use chlorine to do that. See how to Convert Your Baqua Pool to Chlorine.