I don't understand the tumbler thingy.
I think if you are c*child person, they are familiar with some funcy device that "tumble eggs" which basically rotate the eggs in mid water powered by some air pump. The cheapaskate I am I just make them out of plastic pop bottle. I don't know if you do hatch brine shrimp but some people make the hatching container out of 2 lt pop bottle. Same concept but I make the egg tumble with smaller plastic bottles(since I get enough batch of eggs).
Anyway, you invert the bottle and cut the couple of inches of bottom(now top) of the bottle. And basically put the airtube in it so air bubbles lift the eggs and tumble them. But just stick the airline from the top, it just doesn't tumble the eggs so well. It usually end up collect eggs behind the airtube and stick to the container. So I had to find the way to bubble the air from the bottom to lift the eggs in the mid water. I make the hole in the middle of the wine cork and stick the airtube through it and make it flash and plug it in the pop bottle and silicon it to stay as the bottom of the container(used to be the round shoulder of the pop bottle) retain smooth round shape(the eggs rotate better). I just have to silicon it well enough and let it dry so water don't leak.
I just find the eggs that not stay on the bottom of container hatch better. Like floating rotating eggs are like "rolling stone gather no moss" they discourage the fungus in a way. And I try not to use chemicals to hatch the eggs even fungucide or methlene blue. Also I find some tanning help discourage fungus, it seems. I read about some people using alder cone and thought about it and decide to experiment with some peat water. And it seems work so I now hatch my eggs with some peat tinted water most of the time. Of course, if you do that you have to re-acclimate the frys to non-peated water slowly to the water you are going to keep them. So now I usually use the peated water first day or 2 and slowly dilute the peat as the day goes and try to get to the water I am going to keep the frys before they hatch.
I will just keep trying until I find what works.
I am going to order the C. melanotaenia from Bryan now, I think, with some of his green neon lasers, gold cardinal Tetras, wild pandas, and others he has on hand to replace some of the ones lost this year.
Gee, you really make me want to get the fish from him. He has gold cardinal tetra, too? Although I haven't see the picture but I imagine they must be selectively bred crdinal similar to the "gold neon(lutino neon)" which I have some and almost big enough ready to try breed. I bred regular kind about a month ago and I have about 2 dozen of tiniest Neons right now sharing the nano/fry tank with cory frys and red cherry shrimps, oh yeah and many snails.
I done with Neons more than few times but I never bred Cardinals, heck I never owned them. And I always wondered how difficult to breed them(I hear it is difficult). Although I have to organize and make some tank space. And all the frys from Melanotanias now. I find they hatch, I mean they hatch really well. Like 95% of eggs now unlike Sterbais'. Their eggs are about same size. And they start to lay 100+ eggs every 4~5 days now. I don't think I have more than few weeks old but. I might have tons of them in few months. And I don't know how popular they gonna be. I know I can never have problem with Pandas and Sterbais(I haven't got much off spring considering the all the eggs I collected) but I just don't know about Melanotanias. I guess they are pretty prolific, after all they probably belong to the Aeneus. Did I tell you I got 147 eggs from them yesterday? And I expect most of them to hatch in few days. Of course depends on the stage and size of frys but I don't think I have space for more than few hundreds of cory frys. But the way it seems, they may produce a thousand frys in few months if not sooner. This maybe a problem. I might be looking many foster families for them in this fall winter. And I only have 2 females and 3 males. I guess I just have to wait and see.