You asked about algaecide. Most here will tell you not to use it ever, as it is not necessary. If you want to use it to be aware that there are multiple kinds of algaecide. Never use the ones with Copper Sulfate, (or any chemical with copper) as this will cause staining, and blond people to get green hair. If you really need to use algaecide, use Polyquat 60, but this is best to prevent algae, not to kill off an active bloom.
With regard on when to add chlorine, this is important to understand the logic behind the answer. I will try to explain.
OK, for the sake of argument so you can look things up in a table, lets say that your CYA number is 50. Here is what the tables say about your FC.
Minimum - 4
Target 6-8
SLAM 20
So anytime that your FC drops below 4, you will start creating algae blooms. So you need to add chlorine as often as necessary to make sure that you never drop below the minimum. Realistically, try not to drop below the bottom of the suggested range of 6.
It is safe to swim up until the SLAM level, so if your FC measures 20 with CYA of 50, it is safe to swim.
I like to think of the target as what you should start with and end with, so at 8am have 8, at pm you might be down to 6, then add more.
You need to learn how much FC your pool will consume on a day. I know that on a sunny day with no swimmers my pool will consume aabout 1.5-2ppm of chlorine.
So my logic, is that I put my FC up to about 8 at dusk, once the pool is closed for the night. A clean algae free pool will not lose any FC overnight, so if at sunset there was 8ppm of FC, then at sunrise, there will be 8ppm of FC. I know the sun might takeout 2ppm of FC, which drops me down to 6, which is still in great shape.
Now lets say I was having 10 people to swim (in a socially distanced way of course). From past lessons, I know that peoples sweat, sunscreen, urine (god forbid) I might use 4ppm of FC. Well, as long as I started with 8, I would be OK to lose 4, as I would not drop below the minimum. Now I dont like to cut it that close, so I would probably start my day at 9 or 10 if I were going to have that party, just to be safe.
But all of this normal consumption rules will be set after the water is clear, and you have passed the SLAM criteria. Until then, all bets are off, and you need to check FC multiple times per day and add as needed.
If it helps, think of your pool like feeding a child. You might know that your kids will eat 14,000 calories in a week. But you cannot feed your kid one meal of 14K calories, and then not feed them again the rest of the week. The same goes with your pool. You cant simply dump in chlorine on SUnday, and think that you dont have to do anything until the following Sunday. YOu need to feed your pool FC every day, just like feeding a kid or pet.