I haven't had any luck tumbling bangai cardinals eggs either of the times I've tried. I think it's crucial to let them hatch before you take them from the male. The first time he spit when I was catching another fish in the tank, the second time I was trying to move him into a refugium to give the fry a better chance at survival. The next time they spawned he carried them 22 days, spit them, and the female must have eaten them. They were the only fish in a 40 gallon breeder FULL of copepods and amphipods. Ungrateful wretches!
I realize that doesn't help much, but I'd recommend against methylene blue for them, just knowing how much more sensitive they are, personally. I've tumbled literally thousands of cichlid eggs. There was a big difference, besides the fact that they're hot pink even .