Usually I associate browning/yellowing tips with a soil problem. It looks like it's planted in an OK medium, but I wonder about this:
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What do you think is causing the algal growth immediately above the core of the rootball? I'm guessing it staying wetter than the surrounding soil. Lots of people will tell you that if you use a colander like what I think this tree is planted in, your soil will drain better. But it's just not true - it will drain FASTER, but not BETTER. Your soil determines how much water is retained, not the pot. Think about your soil as though it were a sponge. If you placed a sponge in a pot, would it hold more or less water than it would sitting out on your counter? Of course we'd all recognize that the water in the sponge doesn't care if it's in a pot or not - it holds exactly the same amount of water. It's exactly the same with your soil.
So one reason it could be staying wet and causing the algal growth is that the core of the rootball still possesses the old field/potting soil it was originally grown in. An overly wet rootball core could also cause all the browning/yellowing needle tips you see. All the fungal treatments in the world won't help this situation. Do you feel as though you've carefully removed ALL of the old field/potting soil in the rootball and replaced it with the pumice-based medium we see?
Scott