What acidifier did you use? Most of them take quite some time to make an impact. For potted plants, most people would add a small amount of vinegar in their watering to adjust pH.

Citrus are a bit picky in the transition from outdoors to indoors. Lemons in particular, do some yellowing and shedding when brought in. I would guess it isn't your acidifier, but just the transition phase for your lemons.

I used the Espoma Soil Acidifier— is that not good for citrus?

How often do people generally water for indoor lemons?

I doubt that your soil needs acidificatuon. How do you know it needs acidification?

Asking "How often do people generally water for indoor lemons?" is like asking "How long is a piece of string?" Meaning that there is no set answer. Watering frequency depends on the soil mix, relative humidity, temperature, size of pot, size of tree, type of tree and probably other factors. My watering frequency now is every 3 - 6 days.

You do not need to flush because I see no evidence of salt build up.

If you are seeing yellowish leaves and they are only older leaves (at the bottom of the tree), then you need not worry because plants discards old leaves that are no longer functioning as they should.

Your tree looks healthy, so don't worry.

By the way, watering with added vinegar will drop the pH, but only very temporarily, so doing so accomplishes nothing.

you tree is still very stressed form moving it indoors ...

i would let it get over that and the two additional remedies before you go heaping more remedies on ...

big city name... how long has you furnace been running non stop.. that your house is so dry you need to run a humidifier??

was there any cold event before you brought it in... doubt it.. but may as well ask ...

i would be very leery of a lot of fert in winter ...

is that black can above the tree the light source ... how intense.. and how long do you run it .??

things with trees.. happen in tree time.. counted in years or even decades ... think of all you have done to it.. in the few weeks since you moved it indoors ...you might be hard pressed to figure out what the problem might be.. if you havent already fixed it ...

ken

Thanks everyone, I had tested the pH and thought it was a bit high and also used a moisture/pH meter. Though, I guess they’re not the most reliable.

The yellowing leaves are actually at the top, and not bottom leaves. Some of them are probably older, stunted ones, so can see why they’d drop.

But, will wait and watch as advised!

Just one more question, why would there be a secretion coming from a flower bud? I’ve checked for pests and have not found any. Have received multiple answers— some say it’s normal and others say pest. Any ideas?
It’s like a sap, slightly oily/tacky/sweet.

You have pests, you just can't see them. Either thrips which hide in the flower buds, or spider mites in which you will need a magnifying glass to see those.

Vinegar does help make nutrients available to my trees and many others in whom I have encountered, same for any gardenia, jasmine and many other plants that do not like a high pH watering solution. My tap water stinks and if it wasn't for that, most if not all my trees would grow yellow.

I just sprayed with the whole tree with miticide last night. Is there anything specific I need to do for the buds? I’ve never had thrips before but know they can be devastating...

I would soak the whole plant if I could in a soapy water for a bout 20 minutes. The rinse it off.
If you can’t then at least sink the pot under water then spray the whole tree with a horticultural oil like ‘ All seasons dormant oil’. That will kill everything you can’t see in the soil and in flowers and on leaves.

I’m unable to soak the pot, it’s much too large...
I also sprayed the soil with neem and all of the leaves. Can I do a different soil drench of some sort or just constantly spray the entire plant?

I’m inclined to think spider mites because I think I saw one strand of a web. But would rather be safe than sorry

Get some horticultural oil like the all seasons dormant oil, doesn't have to be that brand as long as it's 98% mineral oil. Hort oil in my experience works much better than neem. Spray in the evening or whenever your lights turn off.

Thanks!

How big is the pot???

It’s probably a ~14x14.5” planter