Don’t be discouraged. I know it is heart-breaking to get them so far and then have them expire, but you learn from each attempt so you have gained something very valuable.
I have the new Seio pumps on my pony tank. They have a good flow but it is more dispersed and mellower flow. You might try pointing your flow towards the front glass or a large rock to slow the pressure of the water?
Wait ’till the experts come to help? You are not doing anything wrong, you are just learning. The hard part of SW fish breeding is that we are the pioneers!