Not enough information to answer your question. WHERE ARE YOU LOCATED?, for starters. Watering a healthy Canary Island Date in the HEAT of high Summer should not be an issue unless you have inadequate drainage...., BIG DIFFERENCE, these palms actually LOVE WATER. Has there been rainfall? Post a picture too.

Can't edit the original post, so I'm adding photos in this comment.

Location: Southern California (Orange County)

It has been hot and dry, but the problem started around the time I watered it heavily via a pipe that goes about 4ft deep

Well, normally hard to rot the roots of most palms, but it is certainly possible... is soil a nearly solid clay? If so, root rot is likely.

Yes @palmbob, the soil is not good - clay and rocks.

This is new and totally looks like fungal spores or something:

I'm in Palos Verdes about 2 blocks from the water and I too have rocky clay soil, although I have found out that it drains pretty good. I planted a Triangle Palm in August of 2015 and it is doing well, I water it for 2 minutes once a week, sometimes once every 10 days, depending on the weather forecast. Phoenix Canariensis and Triangle palms like relatively dry soil, so I'd stop watering it for a while. Why did you put a pipe 4ft deep?

Put a pipe when I just planted the tree 3 years ago, did it so I can water it deep instead of soaking the top layer hoping it seeps through

If you hadnt said it,I would have guessed it went too dry. Is that real or fake grass? If its fake..that newly planted palm is just going too dry.

Now,IF you added fertilizer to the water? THEN you might have burned the palms roots. Just water more and wait to see if it outgrows the damage.

I mean,too much water in soucal in the summer doesn't sound right.

Or..both. The fake turf and not enough water...THEN you poured fertilizer water on a root system kept too dry.

Like I said though,it doesnt look seriously burned. More water to flush and roots re grown and its fine.