And buckle up - the SLAM process can seem like a long ride. It is never a quick fix. You will have to buy a lot of liquid chlorine (and not substitute anything else!), and commit to testing very frequently. As much as initially every 3 hrs during the day, if possible. Test, determine how much liquid is needed to get back to the target, add...wait a bit ... and repeat. Brush frequently - daily or more often. Filter will have to be cleaned as it gathers the debris. Life gets in the way, but the downside is then the process will take longer. Over time, the frequency of testing/adding will reduce, as more and more algae gets killed. There will be deep cleaning - taking out ladders, taking off lights, scrubbing skimmers, etc. to get all the places algae can hide and be safe from Cl.
Sorry to say, but your pool guy did more than let you down, he created a big mess that will require a lot of your attention to fix.
We can help on reducing the pain points in this process, but it will take some serious effort on your part to get it accomplished. Some need a week, for others it stretch's out for weeks - it all depends on how bad the initial conditions are, how dedicated one can be to the process, and not getting fed up and ending it a bit too early.
Read up on it here in the various Pool School and Wiki entries - but going forward, AFTER you have fully defeated the algae, there are really only two paths to take to keep the pool perfect.
1. Daily testing and adding of liquid Cl. Every day during the warm season.
2. Convert to a Salt Generator. It requires a highish startup cost, but has been proven over and over to be a huge long term saver in cost and maintenance time.
Robots have their place, but for the immediate need, save the money and put it toward conversion to a Salt Generator. During the current process to get rid of algae, it will just be another thing to have to frequently clean and maintain as it gets overwhelmed.
Just a brief side note - I was a multi-decade tablet user. I was unknowingly on the treadmill of the tabs adding too much CYA, that then required more tabs. I fought green constantly. There were few days where it wasn't green or cloudy over the years. Many, many, many hundreds of $$ each year. A good week was only needing 2-3 hrs for "pool stuff", usually a lot more. Now, with a better filter (like yours), and a SWCG - I will spend maybe $100-$150 on chems for the year, and never spend more than 1/2 hr a week dealing with the pool....and no robot, I still brush and vacuum manually.
