This is my money tree - Cash Buckley. Any idea what's wrong with him?

Cash Buckley lived in my living room for the first eight months after I got him, then moved into an office space. He was re-potted from a 10" wide pot to a 16" wide pot immediately upon moving into the office. He was thriving before being moved, but since he's been in the office (about four months) he's been on a slow decline. More information as follows.

Plant type: Pachira Aquatica Money Tree

Owned for: Eight months before sickness.

Been sick for: Four months, considerably so the last two.

Re-potted: January 2021 from a 10" to a 16" wide pot. This is also seemingly when he started his slow decline.

Soil: The soil he came with plus potting soil left over from a previous plant that had died, that I added to his soil when I re-potted him into the 16" pot. I took the dead plant and roots out first. I used Jobe’s Houseplant Plant Food Container Spikes about two months ago.

Water: I was watering roughly every month, recently switched to every two months as I was worried I was over-watering him. When I water, I just use a plastic watering can and pour over the top of the soil with lukewarm tap water.

Light: Indirect but full light, as he's placed about five feet back from floor to ceiling windows. The building faces North, so the sun never actually comes in through the window. He gets artificial LED at night (office space).

Pot information: 16" wide pot, has a drainage tray built into the bottom of it. I don't empty the tray, but I don't think I put so much water in that it would be an issue of the roots sitting in water.

 

Almost certainly lower light levels -- the plant isn't getting enough light to even sustain itself. Like us, it can live on reserves for a while, but it soon begins a decline if it can't handle it.

 

Plants feed from the sunlight. Without light they starve to death.