I can't speak to the mold, but checking out that mulch pic it looks like the bag is way more sapwood (splinter-y, non-bark pieces) than pine bark. Sapwood retains water differently, takes up space different, and tends to sap nitrogen--it is recommended to minimize/eliminate these pieces from the mix. It's tedious as can be, but for perspective it takes me 2+ hours to fully sift through one bag of mulch (sieve out the bigs and the fines) and pick out sapwood. My plants in 5-1-1 are thriving, and seem to well-tolerate watering neglect (it has been hard to under water them so far as long as i tend 1x/week).

Of note--is there some degree of clearance between the bottom of your pot and where it drains into? Blocked drainage holes prevent air-flow--you might find that your pots dry faster if lifted a bit to expose the drainage hole.

Thank you for the comment. I gave up on the mix. Too many what ifs and realizing,just as you pointed out, it is sapwood.

Im making a true 511 now. It is currently liming. Fingers crossed i can get a plant to survive in it lol.

You're welcome! This post randomly showed on my sidebar, I didn't realize it was 2 years old!

Good luck with your 511--here's a picture of my most recent batch:

This may be too little too late, but figured I would chime in anyway in case OP continues to play with bark based mixes. I also live in metro Phoenix and use the bark from HD linked above. I don't really screen it though, that always seemed like too much work.

I have found that I have to take watering schedules with a grain of salt. So many other factors go into it. What you are growing, what rootstock it uses, the size of the mix relative to the rootball, etc. I have a peach tree in 5-3-2 (bark:perlite:peat). The rootball takes a big portion of the pot. I water this daily in summer because it struggles when I don't. It's always been less fussy than my citrus. I have some sour orange seedlings in small propagation trays. I also water those daily and they are very tolerant of my watering habits. My meiwa kumquat (on macrophylla) is in the same 5-3-2 mix and gets water every two days. It's rootball doesn't fill the pot as much as the peach tree. It's also never shown me symptoms of overwatering. My Meyer lemon and Ruby Red grapefruit, purchased from the big box store and so likely on C-35 rootstock, have been tricky to water properly. These have been in larger pots relative to their rootballs. Historically, I could not water them more than twice a week in the summer without getting yellow leaf drop. This is the first summer they have really thrived. They look full, green, and happy, and have been actively growing all summer. Usually I just hope they survive summer. This summer I've watered them every two days. I don't know if they are just more mature now, their rootballs are bigger, or for some reason every other day is their sweet spot (I've tried this in the past to deleterious effect).

All that to say, I've never found the blanket statement that you can water unrestricted to be true. But, you can have success with that bark. Several factors, like tree, size, and container will also impact your watering needs.

Finally, I do question your watering practices. 5 seconds with the hose nozzle does not seem like an adequate watering. Most of that is probably running down the sides. It's frequency, not quantity, you have you watch out for with overwatering. Really drench that rootball. Then let it sit for a few days. I bet if you pulled the tree out after a 5 second watering, you'd find the rootball completely dry.