[ThRoewer]

When I was trying to raise fridmanis in the 90s I used a separating funnel as a tumbler. Though I cut the top off slightly above where it is the widest. And I actually pumped water through it to keep the egg ball afloat and not air. Though that requires a bit more complicated setup.
See how long it takes for the eggs from spawn to hatch. Once you have that it is best to steal the eggs the evening before the hatch.
Success in rectangular tanks will be less likely. I would suggest an octagon on the side to get a flow that is more like in a planktonkreisel as it is used to keep jellyfish.
You will also need something better than rotifers and brine shrimp to be successful.

I got them no further than 3 weeks. I'm sure the failure at that point was due to the one-sided brine shrimp diet.

BTW, there is a book out about breeding these guys though it isn't particularly helpful on the feeding procedure as Moe (the author) used primarily wild-collected plankton (one of the perks of living in coastal Florida).