I've never used any type of algicides or other chemicals in my pool. Super shock it before winter shutdown, and the water is crystal claer when uncovered. Hell, I put so much chlorine in before the winter, that when I took the cover off and set it on my lawn, I burned a perfect 30 foot round circle on my lawn last week. (I hope the lawn comes back to life)
Now of course, after a day or so of the sun hitting the water when the cover comes off, the water turns green.
I uncovered and started to fill with the proper level of water last week. Crystal clear water. 2 days later, the water was puke green. Super shocked the whole mess, set up the filter, ran it for 24 hours, removed the filter element, hosed of the D.E., re-charged it and went swimming this weekend in crystal clear water that tested perfect on a test strip.
I think that algicides put another part into the equation that doesn't need to be there. Now of course, I am not a pool man, but it work for me.