Algae is the canary in the coal mine telling you your water isn't safe to swim in. Algae itself isn't dangerous, but it means there isn't chlorine to fight the bacteria and viruses that get into the water. Each person in the water brings in some fecal matter. That sounds really disgusting even though it's usually a trace amount...But Chlorine blasts it apart to make the water safe. No chlorine, no way to kill bacteria. Plus, at high CYA levels like yours, you need far more to kill all that nasty stuff.
I'm sorry: There is no way around this.
"Shock" is a word to describe powdered chlorine and is usually Di-Chlor. With your CYA level you should not use Di-Chlor or Tri-Chlor (the tablets) again unless your CYA level is low. Both dump tons of CYA (stabilizer) in your pool and that makes YOUR situation worse and worse.
The other powder called "Shock" is Calcium Hypochlorite. You CAN use that but unless it's 60% or higher (48% and 68% are the usual levels) I think it's more trouble than it's worth. Cal-Hypo, the stronger stuff, CAN clear up your pool, but can also make your water cloudy (milky cloudy isn't so bad. Green cloudy is VERY bad).
You can listen to your relatives or us. Not both. Your odds aren't good if you keep tossing in packs of "shock" and it's di-chlor.
If you don't care about fading your liner, you CAN raise your chlorine level very high by adding 15 gallons of 6% bleach immediately, which should raise your chlorine level to about 30ppm (you need to get it to 25ppm just to reach shock level).
Or you could get 12.5% Liquid Chlorine and add 7 or 8 gallons, again, you may bleach your liner a bit.
It's your choice. If you want to protect your liner from fading, you need to keep FC at 25ppm for several days. If you don't mind it fading (like me--my liner's old) you can over-dose it with bleach or LC. By the time all the algae is killed, your FC level WILL have come down.
Still, it's very hard to take care of it this quickly.
If you get it cleared up, you should look at our B-B-B method of pool care. I haven't shocked my pool since early May and it's now July. Why? I understand and follow the B-B-B method. I don't think ANY of the Mods here, or our senior members, shock unless they have a reason to.
Carl
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