There is no algae that cannot be killed with chlorine.
Your algaecide is made by PROtech Pool Chemicals, which is owned by AllChem. It is the exact same chemical that everyone else sells. It will not work on heavy algae growth. Contact the manufacturer and ask them if you want. They will tell you that the product is not for clearing heavy algae growth.
There's a big difference between actually working on pools and sitting in a pool store selling people chemicals.
When your advice doesn't work, you just find a way to blame the customer and sell them more chemicals.
People who actually work on the pools need to get results. How many hours do you have on-site in the field?
Here's a little educational info for you...Allchem, is not a manufacturer and do not "own" PROtech chemicals...they are a distributor. I do not "sit" in a pool store selling chemicals, we offer advise, give pool owners the necessary knowledge and they make their own decisions, we do not push chemicals that aren't needed like most other stores. You obviously never dealt with us as we do not "blame" the customer and sell them more chemicals, this is a laughable sales tactic put in place by large box stores that have profit only in mind. Your are a complete idiot if you think your advise is anywhere near good, regarding on-site, it's rather funny you mention this as we have service companies that actually come to us when they are stumped on an issue, as well as inspecting commercial properties such as parks, etc...I think my own hours in the field alone, not including my co-workers will exceed yours for the rest of your career (if you're even in the industry).
Regarding your statement "there is no algae that cannot be killed with chlorine". That is the worst statement you have written so far. There is chlorine resistant strands. When chlorine levels are low enough for them to survive, the begin to develop a tolerance. As you raise the chlorine level, they build the tolerance with it therefore the only way to kill them, is with a super-chlorination AND algaecide combo. I think the issue here is the fact that we are retail, you may be a pool boy, and you obviously realize that our free advise is killing your business as homeowners can just look on here, get what they need, and save the $60-120 per MONTH you rape their pocketbooks on. If I were you, I would just take the fact that your incompetent, and pick up a book. A good one for you is "Pool & Spa Water Chemistry, A Testing & Treatment Guide" by Taylor. It has a special algaecide section in there for you on page 35 which may help your reliability! Another really good book is "The Book On Effective Water Treatment" by SeaKlear, page 15 will help you in that book too.