An ultrasonic often has a load density limit. I just mainly don't want the cases forced into contact with one another. Also, the more you put in, the more surface area the same transducer is supplying energy for, so the longer it takes to work.
The cases in my image were run in about 120°F water, too (the 48 in the second photo is 48°C or 118.4°F, which is all the heater could get to at the room temperature then in the house). With the ultrasonic running at that temperature it only takes about 15 second for all verdigris to be gone in the 5% solution. However, it took more like half an hour for primer pockets on that old ammo to be 100% clean, so that's how long those cases were in there altogether. The useful thing is, that shows that even with that much time involved at that acid concentration, the brass isn't being attacked.
I was also using a rack with that 2.5 gallon ultrasonic unit that held the cleaning mix and the rinse water in beakers suspended in the bath. The glass in the beakers absorbs a fair amount of ultrasonic energy, transferring it with less-than-perfect efficiency, converting some to heat and loosing some to the plastic rack as heat and some to the air as sound. If I use a stainless perforated rack with the cleaning solution and tune the liquid level to achieve maximum roiling, it cuts the time almost in half. Still, that limits me as to how many cases fit in. I just line them up with bases down and about 20% free space around them. I've also tried this with cases directly on the bottom of the ultrasonic unit, but it didn't seem to like that and performance was lackluster. That may just be how the resonances play out in my unit. It may not be the case with another.
If you want to use a concentrated surfactant, Kodak Photo-Flo is another that a few drops will do for. Back in the day of darkrooms, there were a number of good ones available. At a couple of teaspoons of citric acid per gallon, you would be making a disposable use-once solution.
Still, citric acid is cheap. I buy mine from
Duda Diesel, an alternative fuels supply outfit. For $27 they send you 10 lbs, postage paid. That's enough for almost 23 gallons of the 5% mix. They got my order to me in about a week.
Incidentally, citric acid may also be used to
passivate stainless steel. If you have something made of stainless that nonetheless picks up rust spots on the surface, that's due to free iron from tooling or other contamination and you can passivate the steel by eating the free iron off the surface. The right concentration for that is usually 10% and you have to degrease first. The best temperature depends on the type of stainless steel you have. The article in the link covers that.
The Wikipedia says that 6% citric acid solution will dissolve water spots off glass. It doesn't say what you do afterward, though I can tell you that rinsing with distilled water is the answer unless you want to use tap water and dry with a dish towel. The choice is just about how old-fashioned you are comfortable with being, I suppose. I can still remember my grandfather drying the dishes with one. Grandma cooked; granddad did the dishes. Surprisingly modern in retrospect, considering they were born circa 1890.