The Tropical Fruit Forum

I am also interested in gypsum, what tipe of gypsum is generally used? Does the builders gypsum, the one that combined with water hardens up, can be used for amending?

Gypsum is Calcium Sulphate, It can be used to supply Ca and S. It is useful as a non lime form of Ca. i.e. not Limestone or Dolomite Lime.
Gypsum will not push up the pH like lime because the Sulphur balances the Ca. In pot mixes up to about 1 kg of Gypsum per cubic metre will not alter pH.
The finer the gypsum particles the greater the reaction. Coarse Gypsum particles act as slow release. Fine powder will be used faster.
You can even bust up Gypsum based building plasterboard for a source.
Natural Gypsum is mined from deposits.
Phosphogypsum is a byproduct of Superphosphate, which is derived from phosphate rock. It can contain heavy metals etc.

When I first started investigating pot mix fertilisers, I often over did amendments. That includes an episode of top dressing Citrus rootstock pots with a good handful of coarse,  "slow release" Gypsum. Over time it severely set them back. The rate was too much, and burnt the roots.
Now I would calculate the amount to apply based on the size of the pots.

Calcium carbonate is basically limestone dust, the most common source.
In horticulture it would be used to supply Calcium and increase the pH of soils or pot mix. i.e. to pH balance acid bog peat in pot mix.
Generally the finer the powder, the more pH reactive it is.
Not sure I would be rushing in to apply it to tropicals, unless your pot mix is low pH.
I think many species prefer neutral to slightly acid soil.
There are other Calcium sources that don't alter pH as easily.

Usually fragrance is more pronounced at male stage. If I'm pollinating, I usually do it when the flowers first open, if you break a petal to mark the pollinated flower and see that the pollen is well adhered to the center of the flower, you're usually good to go.

Hello! I was given this bonsái and determined to save it if possible. I guess I’m just asking if it’s a waste of time or if it looks salvageable. I am very new to this and all tips/advice appreciated!

Great news.
I have found that the smell of the blooms can sometimes mimic that of the fruit aroma, that said the fruit aroma can vary dramatically year to year, so it's not always an accurate reflection.

I'd be a little concerned about the narrow crotch angle at the bottom branch, as cherimoyas tend to split when carrying heavy crops.

It may take them a little time since its a rock. What I've found is that when I propagate new babies the youngsters will show deficiencies for a while before they start doing their thing. During this period I like to hit them with micronutrients and calcium 3-4 times a week. Once they get going i hit them once a month. I use down to earth products. Their liquid calcium and micronutrients are great in spray form. I've grown 110lb racks. Keep on feeding and watering them