Miltoniopsis Orange Rot Problems

Описание: Here are 2 of my miltoniopsis. One which I re-potted right away, the other which I have left in its original medium - which it has been in for about 5 months or so. I don't know what this mix is, maybe pro-mix, or something similar to it? Most all of the orchids that come from my local Trader Joe's are potted in this mix, and I have trouble maintaining orchids in it because it stays so moist for so long. It is extremely easy to over water, and it seems like there is a fine line where a lot of my orchids will then drop their flowers because I'm not watering them enough (out of caution to avoid the roots rotting from being too wet). So in the past I have repotted orchids I buy in this mix right away. In the video when I pull the miltoniopsis out of the pot, you can actually somewhat see that all of the roots are actually dead. :-(

Also, when mentioning water hardness, I had a look through my notes and found that my water tested to be 23 grains per gallon of hardness, where above 10.5 is considered very hard. I have the humidity around 70% most of the time, and I have a fan going to keep airflow around the plants as well. The new growths still get that orange rot on them.. and I am not sure why or what else I should be doing differently. Any help would be greatly appreciated! Thank you for watching!