Andy Sager
Aquarium Advice Addict
The bubbles are to imitate the fanning that the parents should be doing. The theory is that it's some extra oxygenated water to help the eggs plus it prevents any dirt that is floating in the water from settling on the eggs which can cause them to die. Is it necessary? I've had more success using this method than any other way (including leaving the eggs with the parents.) Every non mouth brooding Cichlid fish fans their eggs so I would say it's necessary if you are going to hatch them on your own.
As for when to remove the slate, not all eggs are going to be fertilized so it's not unusual for there to be some dead eggs in a spawn. If the parents don't pluck them off, then you can. Again, this is a learned behavior so it takes them a few time to learn it
A first white egg is not really a reason to remove the slate from the parents if you are letting the parents hatch them out. IMHOAs for your pair, Some Angels get it right the first time, some get it right the 3rd or 4th time and some never get it right. The good news is that a healthy pair of Angels will spawn as often as every 7-10 days so they have many opportunities to get it right. As I said before (possibly on another thread
) you only need 1 wiggler from a first spawn to confirm that you have not only a male and female but that they are also fertile. I would suggest you not give up on any future spawns until all the eggs are white or gone. If these are 2 females spawning (which can happen) the eggs will never hatch. If the fish are sterile (which can happen from all the inbreeding to the specie or some foreign breeders) you need to know this so you don't waste your time or get overly exasperated or frustrated. Once you have the wiggler, you can then decide how many tries you want to give your pair to get it right before moving forward, possibly replacing one of the fish. Hope this helps
