Discolored Phal leaf edges

[sweta]

Hi everyone,
2 of my phalenopsis have developed uniform discoloration on the leaf edges. One is a mini phal and the other one is a large one. The large one I recieved as a gift and it already came with discoloration on leaf edges when I got it. The mini one was very healthy and it rebloomed for me this year but suddenly I'm seeing this sudden discoloration on the leaf edges....both are potted in orchiata bark, sphagnum moss, perlite and charcoal. Temperatures in our house are 70F. Water them weekly and fertilize once in 2 weeks. The only thing that has changed is that I'm sometimes watering with tap water earlier used to use rainwater. Also the window sill where these plants sit get some direct morning sunlight occasionally. Please let me know if this is something to worry about and what can I do to protect these orchids...should I isolate these plants? I'm attaching some pictures. First set of 4 pictures is the mini phal

[estación seca]

They don't need any direct sun ever, though I'm not sure that is the problem. I also doubt the tap water is the problem.

The linear crack at the midline of one leaf suggests a period of underwatering at some time. This could also cause dying back at leaf edges. But I'm not sure that is the problem, either.

Being close to the windows, they might have been a lot cooler than the room on winter nights. I wonder about that.

[sweta]

Second phal pictures

[sweta]

Originally Posted by estación seca

They don't need any direct sun ever, though I'm not sure that is the problem. I also doubt the tap water is the problem.

The linear crack at the midline of one leaf suggests a period of underwatering at some time. This could also cause dying back at leaf edges. But I'm not sure that is the problem, either.

Being close to the windows, they might have been a lot cooler than the room on winter nights. I wonder about that.

Yeah it does get cold in the night and we've had sudden fluctuating temperatures past few days. These plants have always been on window sill even during the winter and they've done ok. But maybe fluctuating temperatures? When weather is slightly warm I open the windows for air circulation. Also I've removed them from getting any direct sunlight

[estación seca]

The second photos show a leaf scratch. The developing leaf has extra pigment, which is common in Phals. It also happens when they get a lot of light. The discoloration along the leaf edges I''m not sure about. Realize hybrid Phals do much better at hot temperatures. Try hard not to let them go below 60 degrees F, and 65 F is better. Many people in cold climates put them on heat mats for the winter.