Hmm, I also want to say overfeeding but it doesnt' seem like it? The last spawn, I fed microworms for like the first week, then went to decaps, golden pearls, and 3 other different powdered foods. (bought off of AB) I fed about 3-4 times a day, I probably overfed, but that's what I have snails for. I've never fed egg yolk, so I can't really say on that :/
I think I'd go ahead and set up a drip to fill the tank the rest of the way. I also agree with trying to feed in smaller portions, but more times throughout the day - like I think you said twice a day you are doing yolk? Maybe do half of what you were doing at one feeding, and break it all up into 4 feedings instead.
I would like to say SBD problem as well, but I don't understand if they had SBD then they would only be floating at the top and struggling to get down? Though bucking is very confusing. When you first said "bucking" I thought of them being very you as of less than two days old because fry tend to get a little ahead of themselves at that age. Have you observed anything else?
Mine usually float at the surface after they've gorged themselves but I've only fed bbs and micro/walter/banana worms at that age. When did you offer them the first feeding of crushed pellets? And what kind are they? You may want to stick to dry foods that are geared towards fry since they tend to have fewer grain products (and are therefore less likely to cause SB issues).
As mentioned previously, feeding several smaller portions should help.
It was just one new life spectrum betta pellet, fed along with some yolk when I ran out of egg and was worried they wouldn't have enough. Right after that they were switched the microworms, and Tisia fed them worms and yolk yesterday. Would adding a few grains of epsom salt help?
I actually sprinkled a bit of the squished pellet along with worms this morning because I wasn't sure if all of them were eating the worms and I was in kind of a hurry, so it might be my fault, sorry >_<
I would agree because you could be treating a problem that needs no treating at all. Usually SBD is easy to recover from but for fry is a bit of a challenge.
Look at this and read the SBD part of it. Also when I read from here, I seen a part that mentioned that most of the time, people don't understand that they can kill fish with using medications when they aren't needed. It was worded a lot better than I remember but that was just my interpretation of it.