Actually you don't have to clean the gunk during the first week. . . I don't, even when breeding in a 1g. I only siphon water and refill very slowly. When fry is big enough to spot, then I siphon gunk.
If you feed BBS, they won't usually touch non live food.
Wow all my fry must be hardy then as they are always getting moved out into separate tanks as soon as they become free-swimming. With me it is a necessity as some of my pairs are fry eaters.
I also give them a day to settle in and then start doing daily siphoning and slowly add more water as I usually only start off with 2-4L.
I think slow and steady is the key if you ever have to introduce young fry into a new tank. You really have to use the exact same water or acclimatise them incredibly slowly to avoid killing them all.
I agree that usually if fry have access to live food they won't take food that isn't moving around. It's instinctive in them to snap at anything small and moving so if they have been feeding on BBS they probably aren't going to take the yolk.
I tried siphoning with a small tube but getting around the tank is quite difficult because my small tank has supports at the top for the down drop filter and at the same time watching out for the fry in case they get sucked up too. I guess I have to be patient lol.
Sorry, what I meant was I didn't see them chase after the live bbs. Not sure if they ate the bbs when they sunk to the bottom either. That's why I tried egg yolk. If I leave a IAL in there would that help grow infusoria?
If they were eating the BBS their stomachs would look orange. If they are young (sounds like they are around the same age as my fry) then it doesn't really take much to fill them up.
If there is excess BBS still swimming around at the bottom they should pick at this over the course of the day.
IAL is great I have found at encouraging the growth of all sorts of fry friendly micro-organisms. You can put a couple in and let them slowly breakdown and this should provide some additional food for your fry.
It could be that they are a little too small yet for the BBS. My four/five day old fry (not sure how they compare in size to splendens) are just taking microworms now. Up until then they were feeding on infusoria.
I've found they have to be a titch bigger to eat BBS. Although I know some people feed it successfully to their young fry.
I left an IAL in there now but probably a bit too late cos it might take a few days before infusoria to grow? I should of threw in my old decomposed IAL from another tank into the spawn tank. I was worried it might foul the water.