Day 4 SLAM - water crystal clear, still high chlorine demand. How much longer?

So we got back from vacation to cloudy water. I started a slam on tuesday, water was clear by Thursday evening. However, the pool continues to need extremely high levels of chlorine. I have to add 500ml at 10% bleach every 1.5 hours just to maintain the SLAM level of 16 (it's even been extremely cloudy/smoky, so not even a lot of direct sun). My ONCL still shows 5-6ppm. I've pulled out the light, brushed and vacuumed the pool . Is there anywhere else something could be hiding? I feel like I...

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