Question
I bought an orchid for the first time and it was in full bloom of white flowers,that same week I noticed that the roots were getting moldy black. I decided to repot with new Phalaenopsis mix. I still have the problem of the roots.  
I went for another orchid this time yellow and even though it has beautiful flowers, leaves started turning yellow to the point that now is a single yellow leaf orchid. Just now noticed that one of the leaves of the white flower orchid has a yellow spot.  (Orchids were fertilized and drained- it didn't help.)
Don't want to loose them!Where can I go?

Answer
The white phalaenopsis may have a soot mold which is harmless-- if unsightly.  It suggests you may have stagnant air and humid conditions.  Try a small fan and let the plant dry out more between waterings.  You can get a fungicide for treating sooty mold.

The yellow phalaenopsis has root rot and should be unpotted, dead "mushy"roots removed, and repotted in fresh mix.  If it has only one leaf and that is turning yellow, it may be too late to save it-- but check the roots anyway.  If you do manage to save it, it will be a long time for it to recover new roots and then new leaves.