Help! My phals leaves have a brown ring around its edges

[joxci4]

I have two Phalaenopsis that need some help.

Phal #1: She's a bit older, and has begun a slow and steady decline since I repotted. After its flowers died I repotted in a larger ceramic pot since she was overgrowing the plastic one, put special orchid mix in there, but the pot has no drainage hole :/ This may be its issue. So since it's re-potting the stem has completely died, and there is a slowly growing brown ring around the edge of the underside of all of its leaves. Is this maybe from hard water or nutrient issues?

Pahl #2: Recently bought and named. Came in a ceramic pot, with a drainage hole. This one too has a brown ring on the underside of all of its leaves, which has tinted the complete underside of one of its leaves. Looks like the others are following suit. Also, I noticed one of its older leaves was yellow and kind of mushy. Perhaps a sign of over watering?

For both I use tap water filtered through a Brita charcoal filter, and only water about a cup each, usually once a week. Maybe a bit less for the second one since it's smaller. Once a month I use about a tablespoon of Orchid fertilizer diluted in a bit over a cup of water and split this between 5 of my plants. They both get lots of indirect sunlight, and the room stays about 65 degrees warmer sometimes when I use a space heater.

Please help me avoid the inevitable decline in health of all orchids I've ever owned!! PS. I've even killed bamboo before :/