Here's what I did with the instructions.. ignored them.
I got the best yield using all treated tap water and unless I was collecting bbs, the hatchery had an air stone running in it.
When I wanted to collect the BBS, I'd turn off the air pump & remove the air stone. Then I'd put the collection cup (full of treated tap water) in it's spot on the opening and had a night-light on right above the cup to draw them up. When I collected enough, I'd take the tube off and put the airstone back in and start the pump back up.
No salt in the water, minimal bbs egg shells and I could usually collect bbs for days this way. I used 1/8 tsp of eggs to 1 tbsp of salt to minimize wasted eggs.