All algaecides are not created equal. Choosing the right algaecide for the problem will make looking after your pool significantly easier. If you have algae and are trying to kill it a product like LoChlor Starver which removes phosphates from the water and ‘starves’ the algae is suitable. Especially if the algae has a luminous green nature. Always try shocking the algae with chlorine first. Most algaecides contain copper sulfate as the active ingredient. These algaecides are good for preventing algae. Winterisers have higher concentrations up to 40gm/L whereas the summer or standard algaecides are much weaker. If you have an ioniser in your pool you will already have a copper level so do not use these algaecides. For cases of black or brown algae a stronger algaecide made on a quaternary ammonium base like LoChlor Tropiclear can help kill and prevent the algae from growing.
If you get black staining, frothing water (bubbles) or cloudiness after adding an algaecide then do not add any more for a while. A high copper level can be caused by excessive use of algaecides. Algaecide is based on detergent and too much can cause a froth. In some cases a pool may go cloudy when the chlorinator operates after adding algaecide. This is due to a chemical reaction due to excess detergent. Again, do not add algaecide and it will go away. Add acid to remove staining. You can add water to the pool (and drain some out) to fix this faster.
Most algaecides last for up to 3 months. The most important times for algaecides are in winter when the pool is not being used or looked after as much and in summer when the pool is being heavily used and the sun is making conditions right for growth.
Always check that you are dealing with algae and not a stain. Algae should move when brushed or feel slimy to the touch and you might be able to wipe it off with your hand. A stain will not be recognisable to feel and it will not brush off.