Hi, all! New plant parent here! I hope it's ok that I'm asking about multiple plants in 1 post. If I should break them up into 3 different posts, 1 for each plant, then please let me know!
A little background info: I got these guys around Oct-Nov of last year, and most of them did well up until a few months ago. I water them all on a separate but regular schedule using the Waterbot app on my phone to keep track, and I use a moisture meter to doublecheck if the soil really is dry and ready before watering, adjusting the schedule accordingly. I have them sitting on top of some low bookshelves that get light from a really big, really tall, west-facing window that only gets direct sunlight a few minutes a day when the sun hits it just right. The house is at a constant 75 degrees F during the day and 69 at night. I'm not sure what the humidity is, but I also have a snake plant, a couple pothos, and a fern in the same area as these problem plants, and all of those are thriving without any issues. About a month ago, I re-potted every plant in the house with new soil, but I don't think that has changed anything, since these problems started before the re-potting and things don't seem to have gotten better or worse.
I can't seem to add any photos directly to the post for some reason, so here's an album of all the relevant photos: https://photos.app.goo.gl/H5ngxCPrgEVYH2Ce7
A couple months ago, I noticed the small bottom leaves on my calathea getting dry and brittle and some of the larger leaves starting to curl too. I read that they like humidity, so I started spritzing it with water twice a day, morning and evening, to see if that would help. I waited for a couple weeks, but decided to cut off the bottom leaves, since they no longer seemed to be alive. I'm still spritzing it regularly, but nothing seems to be changing (neither positively nor negatively). Is there anything more I can do to help it along?
My silver philo actually looks to be doing well overall, and it's still producing new leaves. However two of its leaves started turning yellow before I re-potted everything, and I'm not sure if it's due to overwatering or if it's just a normal part of a leaf cycle. Should I just prune them off? If not, then what should I do?
My ZZ plant is in the worst shape. When I first got it, all the leaves were a nice dark green, like the tallest stem currently is. Slowly over time, it started getting sad and yellow. There are a couple stems that are still green and sturdy, but some of them are drooping and fading, and I can pull them out of the soil with no resistance, as though their roots aren't growing or taking to the soil, even though I've had this plant for over 6 months now (it was the same before I re-potted it with new soil). The yellowing stems always seem in danger of falling over. I thought maybe it was due to overwatering, so I've completely stopped watering it for a couple weeks now, but nothing seems to have changed. I'm at a loss for what to do to revive it.
I would appreciate any help at all for any of these plants!