The only reason we use algeacide is to prevent or destroy algae which feed on phosphate. Both being in the water, a regular and weekly dose is required.
A 40% or 50% algeacide is used for weekly maintenance, or to destroy apparent green algae, used with a shock.
Cheap 5%, 10% or 15% algeacides are not strong enough, produce foam and that's about it.
Ignore algae and you will have to shock about every 2 weeks (enough time for the water to turn green).
There is a product to remove phosphate, used on a weekly basis, instead of the algeacide.
There are green, pink, mustard yellow, brown and black algae. To be able to see them, there have to be 1 million per square inch.
Green algae is the most common. Pink, mustard yellow, brown and black algae are more difficult to get rid of and require a 60% algeacide, a shock and a decontamination. (IE: All accessories, toys, etc. which have been in the pool in the last 3 weeks must be placed in the pool, with the solar blanket on top, all night).
Chlorine, even if formulated to help prevent algae, will be spending more than 40% of its capacity to handle algae and since chlorine is the most expensive product and you would have to double or triple the dose, its cheaper in the long run, to use algeacide or a product to remove phosphate and enjoy your pool every day.
There are now a days, products to remove phosphate. Different concentration according to the quantity of phosphate in the water, which algae feed on.They are a greener option and very effectiveé A phosphate test is the first thing to be done.
Weekly maintenance 300 ppb or less ULTRA CLEANSE
More than 300ppb PREP CLEANSE
More than 750ppm (ppb = parts per billion) PHOS CLEANSE PLUS