Help! Eggs been eaten

[valk]

Hi, Just need bit of advise.
My pair layed about 50-60 eggs 2 days ago. My ph is normally kept at 6.5. This morning I found all the eggs disappear. Could the parent have ate all the eggs due 15% water change last night and PH was accidentially drop to 6.3?
What is the normal process for changing water after the eggs are layed?

Thanks

[Zbiljc]

1. You shouldn't change water
2. Eggs can already heached, but pair can placed fry.
3. Pair soon will breed again