i dont understand your thoughts about why you think they need fresh air?

how cold is out outside.. in your z9 UK?

whats the machine next to the plant in the 2nd pic? .. heat ...

you said it was outside ... did it come in before any cold event??

ken

I will try to help if you are still here . A few questions, what is the compost made up of ?, its name if ready made and what and how often do you feed . also do you ever flush plain water through the pot ?

@Epi Phylum , thank you for comment. my epiphyllum still have the same problem. I use cactus potting mix from Growth Technology with added a little bit of pumice. the soil was very compact like hard rock. I didn't feed it often. during summer I feed it once a month and I didn't feed it at all at winter. I don't remember other two seasons. but I don't usually feed it. I have never flush it with plain water as well. every time I watered it I make sure there are water go through the drainage hole but not much will come out. cause I don't want any water sit on saucer for long time. so I give it 700ml of water each time and there will be only a small amount of water will leak out. now I had remove some of its root and repot it with a lot more grits and bark and a little bit of houseplant potting mix.

Hi Jasmine , sorry about delay i dont think i sent ,so writing this again just in case . its good you have repotted. Your epipyllums phylloclades ( not true leaves) have a form of necrosis . The cause is that epiphyllums and others such as xmas cacti absorb too much iron and manganese due to the composts pH getting too acidic . The iron and manganese are toxic when they build up in the older leaves and they start to die , younger leaves are ok . The reaons for the pH drop are the compressed old peat possibly and the use of fertilizers containg nitrogen such as urea and ammonium also the iron and manganese the fertilizer might contain these forms of nitrogen can acidify the substrate ie the peat mix more, Epiphyllums dont like too much acidity and take up toxic amounts of iron / manganese if ph gets too low . google christmas cactus: phylloclade yellowing and necrosis if you want to see what necrosis looks like in xmas cactus ? It looks different in epiphyllums butvit is also an epiphytic cactus . The English epiphllum breeder F.R.McQuown noted a disorder in epiphyllums which he called nitrogen spot / blackspot . it was a mystery around 1965 but he was aware it was somehow due indirectly to nitrogen . In good warm weather flush a bucket or plain water through the pot , this ensures salts nitrogen and iron dont build up causing acidity and toxicity . hope all this helps ? This is the first time i have ever posted anything ! very nerve racking! i am in the uk .Also i am not 100 percent sure on this one but you may concider using Baby bio, its got urea but no iron and manganese listed and at half dose i cant see it acidifying the compost . plus if you flush salts out it should be fine . have you sold on ebay ? i am sure i have seen the picture if your beautiful epiphyllum somewhere before . anyway good luck

@Epi Phylum, I agree I should occasionally flush out the plant and try different fertiliser. what my epiphyllum got is probably virus though. someone post this video on youtube. her epiphyllums' problem look like mine. even my epiphyllum is still growing and flowering. but it lost a lot leaves.

below is how my problem epiphyllum stems look