Sludgy sediment is usually an indicator of insufficient filtration. But while coarseness does vary across machine, getting that at 21 indicates there's something wrong - you shouldn't get that fine of a grind.

I've been there, so maybe you made the same mistake that I made when I had that problem: When you clean the Barratza and take out the white plastic thingamabob, it goes back in two different ways, smoothly. But if your little orange marker isn't towards the front, on the right hand side, your grind will be much too fine :)

I usually do an initial pour to allow the grounds to outgas - about 70-90 grams, pouring from the middle out, in a spiral.

Then two separate pours of ~220g, slow, outside in - I essentially use the water to agitate the grounds a bit by rapidly pouring the last half in tight circles at the center.

And for the people reading this and think "those coffee peeps are weird" - yes, we are. The taste differences are minute. Can't speak for others, but I mostly do it because I like a ritual, I'm happy with any number of pour styles as long as I get my coffee ;)

The reason I picked this particular ritual is because a) I swear it tastes just a tiny bit better, and b) I learned it in a tiny coffee shop in Colombia that I loved to pieces, and so every time I make coffee I'm reminded of that trip.