Help! I've Jinxed Things!!

You'll see it written to do frequent water changes with fry, but that refers more to people with a nursery tank who are feeding the fry lots of high protein food to speed up their growth - high protein food makes the water messy if the uneaten bits aren't removed. Livebearer fry are big enough at birth to eat powdered 'adult' food - that's all I do, scrunch some of the flake up really small when I feed the fish. Maybe the fry don't grow as fast this way but they still grow. Doing this means the tank only has to be cleaned as normal.
But you should do your usual water changes even with fry in the tank. I've always found things like endlers to be almost suicidal when it comes to the siphon tube. They are attracted by it, they don't run away. And fry are just as bad. You will hoover up some fry, it's something you won't be able to avoid. What you have to do is check the bucket of old water very carefully. When there are fry in a tank, I pour the old water out of the bucket slowly then when there's 3 or 4 inches left have a good look for fry. They are very difficult to net out of a circular bucket with a square net