Is there an iron or manganese or sulfur odor issue?
Captive pressure tanks (equipped with a flexible diaphragm) are now usually the preferred choice over a hydropneumatic pressure tank, but when there is any of the issues mentioned, then the direct contact with the air within a hydropneumatic tank, will often be utilized to oxidize the ferrous metals, thereby converting them to a ferric state whereby then can then be removed by filtration.
If there is no iron, manganese or sulfur issue, or when other treatments are utilized to correct those issues, consider updating and upgrading your well system with a Cycle Stop Valve PK1-A Pside-kick Pressure Tank kit which will likely be comparable or less cost than a replacement hydropneumatic tank.
CSV PK1-A kit
CSV Interactive Animation