Hi, and welcome!!
Wth a CYA of 80, your normal chlorine range is 5-10 ppm, with a shock level of 20 ppm. Since mustard algae tends to be very resistant, some folks find that you have to take the chlorine up higher than that. So.. First step is to take your chlorine up to 20+ ppm, brushing the pool daily, and keeping it there until the algae clears and you're not losing any chlorine overnight. At that point you can let it drift back down to no lower than 5 ppm, but if the algae reappears you'll need to take the chlorine much higher.
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