Going Bonkers: Trouble with re-potting and root rot: Please Advise

[SHag42]

Hey everyone. I seem to be having one issue that i can not seem to overcome. Please help me to figure out what I am doing wrong.
The story goes like this. I buy a new plant, it has some root rot. I cut off the bad roots soak it in a fungicide, Let it air dry for 24 hours then plant in potting mix that has soaked over night, wait 2 weeks to water, water thoroughly with a little seaweed, let drain, 2 weeks later I have to unpot again because the roots have rotted. Trim roots, soak in fungicide repot in a even smaller pot, 3 or 4 weeks later new roots and the plant starts a slow recovery.
these are all phal. orchids.

Now a little history of my growing conditions and the potting medium that I use.

I live in North Fl. in a very shaded area the plants receive about 1 hour morning sun and about 2 hours evening sun. No quite enough light because the leaves are a little dark. No where to move them though and they seem to love it once they get started and grow new roots. The humidity is very high most of the time. 55 to 60 daytime and 60 to 85 night. They sit on a covered concrete patio up on bakers racks to keep the air circulating under them. They have decent air flow and my healthy 4" pots need watered about every 5 days.
They are all in clear plastic slotted pots that just fit the roots. The potting mix I am using is fir bark, sponge rock, lava rock and leca.

I don't understand what is going on it is driving me nuts, it is like I have to do it twice to get it right and that is hard on the plants and me. I would love to figure out what is going on.