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What is your current ca level? Are you using this product? How often/much do you do pwc? What test kit do you use to test your ca and have you tried more than one or taken to the lfs to test?
Could be the product you are using is outdated and has become ineffective but I would think any ca additive would have a decent shelf life. Just doing a pwc on a regular basis should keep your ca level above 300 ppm at the very least. If you are using the product I linked to it’s supposed to balance out mg & strontium with the ca. What is your sg & kh level? I’d have your lfs test for mg also to get that measurement.
advancedaquarist.com has some fantastic articles on calcium and general chemistry in your aquarium. IMO, before you start making a lot of adjustments to your dosing and dosing things you may not need to, read up on calcium, alkalinity and the balance these two things need to rise to proper levels