Without a GH and KH test kit, you wouldn't know if it's needed or not. If you can buy a TDS pen, that would help as well to get the TDS measurement.
Remove the cuttle fish bone for now, at least until you get your test GH/KH kits.
A cuttle fish bone doesn't know when to stop releasing calcium, so that will keep climbing, and it could be too much calcium in the water.
Also note that calcium doesn't get utilised as efficiently if there isn't Magnesium as well in a 4:1 ratio (Ca:Mg).
If you have Magnesium sulfate in the form of Epsom salts, then add a little, a pinch or two for a 25L tank. Just make sure it pure Epsom Salts, without fragrance or other additive that can be added for baths.
The impacts of ammonia on shrimp can only surface a week or 2 after. So this is also a possibility.
Report back when you get your GH/KH test kit.