Help! Persisting Mold in All repotted Phalaenopsis and Cattleya

[nuriko1set]

Hello! I am a very new orchid grower. I have a couple of phal. and Cattleya. I am having mold problems in both.
The Phal. is an Equestris 100B, and it came as a very small plant in a 2.5" container. It was already in spike, which has grown quite nicely in the past 3 weeks. However, after i watered it for the first time, I notice white mold under the top root, just a day or two after I watered. So I panicked and repotted. It was originally in sphagnum moss, so I got some NZ sphagnum moss and re-potted it quite loosely. I did trim a couple of rotten roots and to disinfect, I dunked the roots in Hydrogen Peroxide, which I now know is very bad for roots. After i repotted it, it was good, until I next watered it. And again, the afternoon that I watered, mold developed again. So i repeated the process over, repotted, disinfected with hydrogen peroside, etc. And surprise, again, I have mold. So that's when I read about water culture, and thought maybe I need to let it air out side the potting mix. I soaked the roots in water for a day (which i read something is Semi-water culture), and of course the roots became COVERED with white mold. There were very few roots to begin with, as it is a very small plant. I'm sad to say it seemed to have come with healthy roots, and I've destroyed them all!
Please advise me on what to do. I am almost at the point of to giving up on this plant, but really really don't want to. I am currently airing it off right now. I have read about creating a small bag situation where the moisture encourages more roots to grow. Also, I am looking at KelpMax and would like to try to use it to encourage more root growth. I feel that the existing roots are now destroyed, should I trim those off first then try the bag method? If I don't trim, I feel that I should use some kind of disinfectant to clean the mold? I don't think I should use Kelpmax with the existing bad roots, please advise!

And it seems that it a repeated pattern with my Cattleya that I've repotted. I want to say it was the hydrogen peroxide? Since I used it on every plant. I repotted the Cattleya loosely with medium bark mix of perlite, lava, bark and coconut husk. It seems to dry out very fast, also in 3" container with a lot of air holes. I also run a small fan fairly close to the orchids. They are under a grow light as well. So I feel that I've done everything fairly ok, and really couldn't figure out what I've done wrong. I was afraid of watering too much, and feel that the Cattleyas were really dry before I watered. I used to water once a week, but dunking and soaking for half an hour. The pots seem to dry very quickly and the plants looked dehydrated (getting slightly more wrinkly pseudobulbs. So this week, i watered it twice, as the humidity is decreasing from around 50% to around 40% very quickly. I am in the middle of the east coast and have fairly dry winters. I am planning on getting a humidifier to help the aerial roots. It's aggravating to me that the aerial roots of new plants that have just arrived are plump and in great condition, after it's been with me a few weeks, they start to shrivel up, while the inside roots are molding. I am so envious of plant growers whose aerial roots are so plump and healthy.

For the Phal. I realized that things went south after I watered the first time, which I did by running distilled water through the medium (moss), so the next time I watered, I used a water can with a thin sprout and watered near the perimeter of the pot and used a limited amount of water, not even enough to run it through the media. I also have been fertilizing all the orchids with a 20-20-20 at 1/4 teaspoon per gallon, and using only water every 4th week.

Please advise me as to what I'm doing wrong and what else I can do. Thank you so much!