Imagine you’re making a giant salt slushie. You want the salt crystals to be damp at the bottom, not drowning. A good rule of thumb: the water should sit about one to two inches above the salt bridge—that crusty layer that sometimes forms on top of the salt.
If you don’t have a salt bridge (lucky you!), then the water should just barely cover the bottom layer of salt. It’s not a hot tub for salt; it’s a light drizzle for regeneration purposes.
Pro tip: If your tank is a clear plastic one, you can literally see the water line. If it’s an opaque white tank, you’ll have to unscrew the lid and shine a flashlight in there like you’re spelunking for treasure. Spoiler: the treasure is just knowing your water is soft.
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