Mate its a learning curve we all have when first breeding , even with all info about any fish on the internet these day,but sometimes you i gotta make your own mistakes to learn what and what not to do .i breed Angels,Pepper corys and 3 spoon to be 4 different BN
As said above your w/c's are doing you fry no good !.its not treated so chlorine would be a major fact in the homicide,as well as being to cold or hot ,water parameters totally different from tape to tank,but i also see starvation as playing its part in it as well.
Its a very common mistake a lot {including me} make with fry,killing them with love i call it .But it can be remedied.
first doing a 25% W/C in a tank with adult fish is sometime most people only do once a week,you did this daily with fry stresing them by changing the Water parameter way to fast and on empty bellies, and reading your thread i'm guessing you didn't check the temp of the water going back into the fry tank, it only takes 1 or 2 degrees higher or lower to stress young fry,especially on empty bellis.
Follow this rule of thumb and we should see you tanks full of corys in no time,.
1* treat and age your w/c water in a lightly stocked tank over night,making it the same temp as the fry tank and the parameters[ ph and gh ]as close as possible to the fish tank,when you are ready to do a w/c,using an airstone and a metre or so of air hose, trickle siphon the water back in straight from the aging tank to the fry tank if possible,this way the fry get a chance to acclimatise to the slight change to the water never more than 5% daily for the first 2 weeks,included the siphoning off of uneaten food in you 5/10%and do clean the sponge filter for the first two weeks either,it will give them there first meal after hatching, Thats how you should do W/C for any young fry no matter what they are.
The other part is your feeding program,feed twice a day is ok for adult fish but you fry are growing at a rapid rate and will burn up any energy the food gives them very fast,just like us when growing up alway hungry.Feed a minimum of 4 times a day.Newly hatched live brine shrimp or microworms are best there full of protein,Frozen is ok but you need to use an airstone to make it move like its alive so they see it as food,if you cant get there of them there are some good powder fry food on the market but i only uses it as a back up if the brine shrimp not ready in time.
I personally dont do it but a lot of cory breeders all get all their sponge filters and squeeze them out in the fry tank so the fry to eat the micro creator that live in the sludge.Week 2 you can start giving other small foods such as crushed sinking pellets and finely crumbled flakes but wet the flake so it sinks faster
remember they only babys little things are massive to them
o ,more than 10%W/C daily and includes siphoning as much uneaten food as possible off at less twice a day i do morning before work and at nite before i go to bed.W/C in the morning as well
If you follow this as a rule of thumb and we see your tanks full of corys in no time
Pss:One more there a few reason for eggs not hatching ,G.H is too high which will harden the shells so their no longer
pores or to low making males sperm becomes impotent ,ph will play its part here too,,or the female may have chosen a new male who is sterile or neither of them were in the right condition o spawn again so soon n,but that's fairly normal with more young fish
,one of my pepper pair once spawned 4 times in a week when they first started start THink only 7 or 8 eggs hatched out about 50 eggs that week
watch them bit more and you'll learn what they want and need by the way they move around the tank.
well i hope that cleared a few things up for you and we hear some good news and pics of your success