Try a soak with vinegar. The crust is lime(?) or other minerals that the acidic vinegar will dissolve. It should be able to be taken off with a scrubbie, especially after at least a spritz and soak with the vinegar.
Which reminds me my shower head also needs a vinegar soak.
I have tried vinegar but not an overnight soak! I will suggest this to DH next time we clean it
Time is the magic ingrediënt. 
Citric acid also works really well if the vinegar doesn’t do it.
No advice, other than to say your hard water hypothesis must be correct. Because this has never happened to me, with cat bowls or dog bowls, across many years of pet ownsership where I live. We have very soft water here.
You have hard water. You need to soak the bowl with vinegar periodically to dissolve the calcium deposits. Dh does this like every other week when he descales the coffee maker.
Vinegar can be used to clean hard water deposits. You could soak the bowl with 1:1 vinegar:water in a ziplock or bigger bowl
@turtlegirl Or you can do what I do which is soak strips of paper towel with straight vinegar and place them directly where the ring is (I only get it as a ring at the waterline).
You can also try the “cleaning vinegar” if culinary doesn’t work well. It has higher acidity so is more effective, but be careful with it (like, don’t stick your bare hands in it), since it is a stronger acid. This type of vinegar is usually found at hardware stores but not grocery stores (at least around my neck of the woods).
My mom gave me a few of these crocheted pot scrubbers from a church sale a year or so ago and DH finally trashed the last one. I’m going to have someone in the neighborhood make me a few. What kind of yarn should they use? She asked if 100% cotton would work.
I assume that they are what’s called “dishcloth cotton” because it’s cotton yarn specifically for making dishcloths. There’s also some that has scrubby bits, which makes nice scrubbers. I made a bunch of soap sacks out of that.
Anyway, a trip to Michael’s yarn department will do the trick.
Do you think regular 100% cotton would be OK or should I have her get the specific kind?
Obviously this is the complete opposite of 100% cotton, but a coworker used to make them with strips of tulle. Like six inches on a spool, she would use that as the string. They were nice and scrubby. But not at all cottony.
Oh smart!
@noodle There is also a product out there now essentially made from nylon netting that is exactly like scrubby material. I forget what it is called but there are patterns for it as well. I bought some on a lark and made a big scrubby (like bathtub scrubby size) from it. They had many fun colors. Mine turned out like this
I’m not sure if you can see any detail, but it’s crocheted, super easy. You can make the disc type scrubbies from it, and it would be good for extra scrubbing power.
I would say while you can use any old cotton, “dishcloth cotton” (aka “kitchen cotton”) is of a gauge and strength that will hold up and also go faster to make (I think it’s generally worsted or maybe dk?, I’ve also seen it in chunky (which was like 2x or 3x worsted, and which I used to make a bath mat aeons ago)). There is a brand that people say is better than the rest… If I could remember…
Dishcloth cotton is pretty cheap and comes in a gazillion colors. I wouldn’t waste better yarn!
Got it, I’ll find some of that!
I had a swap partner make some of those scrubbies out of the plastic onion bags. It’s interesting that now companies are making the material specifically for crafters.
If I start seeds now when my garage is really warm, do I need to use a heat mat? Or just lights and a humidity dome?
I would only use a heat mat if it was cool, and I have never actually used a heat mat anyway.
My garage is detached and uninsulated so generally the same temperature inside as outside. In the spring I definitely need a heat mat and I’ve never started seeds this late. I will try it without a mat.
