If she seems to perk up after the water change, I would do another one tomorrow morning and see if you can get a test kit. And or get the lfs to do a test, and write down what all the things are.
Ammonia
NitrIte
NitrAte
pH
any thing else they check.
Get Prime water conditioner if at all possible.
What size tank is this
temp
inhabitants?
When was the last water change? before this one?
Do you do gravel vac?
Do you have a filter, what kind/size?
Have you changed the filter pads recently?
Cleaned them.....how?
Also if you are feeding flakes, consider Hikari First Bites if the fry are still very small, or Micro Bites and smash them yourself with the back of a spoon in a dish. Feed sparingly, .....for fry though a couple to several times a day, still just small amounts.
I am guessing possible combination of things.