You must run ACE in soft water only. There are many ways to accomplish that.
If your source water is soft, you're set.
You can buy a water softener - like the small tank-type many folks use for an RV. Easy to use, 'recharge' manually, not very often.
You can use the "Vanishing Act" product which is available through HS dealers. You set it on the return fitting at the bottom of the spa, and take it out 24 hours later. Longer if your water hardness is extreme.
Keep the water soft, and balanced, and you'll get three or four years out of a cell. If you don't keep the water just right, you'll get a couple of years out of the cell - and they are around $700 to buy, DIY install is easy.
HTH