I use softened water at fill up.
I use bromide+bromine tabs and bleach per the sticky here.
I use a Taylor test kit and maintain the water perfectly.
I just did a drain/refill and noticed that, below the water line, the tub looks "chalky".
What is it from and what's the best way to remove it? (it didn't come off with a sponge+Ahh-Some)
The tub shell is a textured plastic, not a high-gloss acrylic.