The Rune of Capacity increases the capacity of the Blood Altar by an additive +20% per rune.
With some Netherite Scrap and some Intricate Hellforged Parts looted from the Demon Realm, you can double the power of your Rune of Capacity, increasing the capacity of the Blood Altar by an additive +40% per rune.
If you change your mind, you can undo the recipe in the ARC.