What is this alocasia missing?

Hi, I got this giant Alocasia from a friend who owns a lot of unusual plants. He gave it to me in a suitable pot and chunky soil (according to his information) and I put it next to a south facing window for light. You can see the windowsill in the pictures, it should be a distance of around 50-70cm. I have owned it for around one month now and since then, the leaves became visibly yellower at the edges. It was already slightly there when I got them, but it has definitely spread. I tried to give them the same care he advised and I bought the same fertilizer my friend used previously. I use it every week at the recommended strength. I only missed 1-2 waterings with fertilizer because I had to buy the bottle first (so only water then). The yellow is more intense on older leaves. I didn't get any new leaves yet, but the newest one has continued to unfurl, but now it hasn't moved for 1,5 weeks (which still might be normal, it was moved when the leaf hadn't unfurled fully)