I would be interested in what others have to suggest as I need to change my soil due to poor growth

Also...Perlite of course. Never rots or breaks down. For Mango I found a good course sand that wont pack down made a perfect soil if mixed with potting soils or maybe firbark. I see many plants now being sold in firbark. Light and not nearly as acid as peat. Peat also breaks down into a goo.

Would the 5-1-1 mix be too acidic?

One great grit? ground lava rock. Full of micro nutrients too. You might go to the local rockery..and purposely go for whats been ground down at the bottom of lava gravels sold for ornamental landscaping.

Stanofh, lava rock sounds great, I'll definitely go out and look for some this next weekend.

Laura, I'll be honest, I'm not sure about the acidity.

I ordered a Pickering mango and it arrived just a couple days ago. Since shipping to Hawaii has restrictions, it was mailed bare-rooted. My mom is here visiting and I asked her to open the package up. I went out with my daughter for a few hours for her band stuff, and when I returned, my mom had already planted the mango tree in a 3 gallon container with some potting soil, lots of perlite, and a bit of sand. Now, since posting this initial question, I'm contemplating whether to leave it in that mix until it it time to pot-up and then in a several months make this gritty mix that I was asking about, or whether I should repot into that gritty mix as soon as my mom leaves- she's almost at the end of her visit this week.... I'm wondering if repotting it again so soon would distress it.