Hello everyone! I have been reading these forums for a couple of months now and I really appreciate the kindness and generosity with which everyone is sharing their knowledge and experience. I need your help!

Of my three rubber plants, two are very healthy and one (the largest one) is fading quickly. All three receive the same amount of light. I had originally put them in containers without drainage holes but I have learned my lesson and now everything I own has proper drainage :) When I repotted I suspected root rot, but the roots looked completely healthy. There were no dark or brown sections at all, as far as I could tell. So I let it dry out and breathe in the new soil for a bit and then it continued to decline. This led me to suspect nutrient deficiency so I began fertilizing with a phytoplankton/seaweed blend. The plant has continued to fade away. I sprayed with neem oil earlier this week to help rule out any fungal/insect issues (which were at least not noticeable during repot).

A few of the leaves are still in perfect condition, but most of them have brown edges (not tips) and they have recently started drooping down. A couple have even fallen off all on their own. The new growth seems to have stalled. I really love this plant and I'm hopeful that it can be saved but I must admit that I do not quite know why this is happening. If this plant cannot be saved then I hope that I can at least learn what happened so that my other two (healthy) ficus' will continue to thrive without any issues.

My soil mixture: Garden Bark Small Nuggets, Organic Potting Mix, Perlite

• about a 1:1:1 ratio, this soil drains really fast but still holds a bit of water. I do let the soil dry out between waterings. I'm tempted to repot with a 1:1 mix of potting soil and perlite, and I also have some Bonsai Jack Succulent mix which sounds like it would be great but I am done experimenting on this poor plant! It is time to seek help!
• Some side questions: when using 'gritty mix' how can you check for moisture levels? My Bonsai Jack mix feels dry almost immediately.
• Would the Bonsai Jack conifer soil work well for my ficus'? The blend looks to be VERY close to Al's recommended mix. I currently have BJ Succulent mix which I can use immediately if it will help, but I will gladly purchase the conifer mix if that would be better. I wish I had the space to buy and mix my own gritty mix, but my apartment just won't allow for all of that next-level goodness. Bonsai Jack seems like a great option.
• Do these types of gritty mix soils work well for plants that like soil to stay moist? I have some philodendrons, calathea, persian shield, arrowhead. Would these all be happy in the Bonsai Jack conifer soil, or should I use a 1:1 mix of indoor soil and perlite?
• Can I use coconut coir in place of pine bark in the gritty mix?

The bottom line: I would love to repot all of my plants ASAP into the best soil possible and then let them continue growing in that for the rest of their long, healthy, happy lives. Let me know what would be best! Thank you all

Here are some photos of the plant in need:

My ficus trio

Help this poor ficus!

Leaf edges

Current soil mix: Garden Bark, potting mix, perlite. This top layer has much more potting mix than the rest of the container. I just used it to fill in and level off the top of the pot.

One of the healthy leaves! I'd love to help this plant get back to her natural beauty!