Are these baby clown fry? If so, I wouldn't change the water right away. What I used to do was use a piece of hard line tubing, siphon off the bottom of the tank every day (after day 2 of them being in the larval tank) and use a little new water matched with the salinity/temp of the larval tank to top it off using a slow drip method. I also made sure not to use too much phyto so that there wasn't a ton of waste.
That's what worked for me, however, there are more successful people on here that are breeders that I'm sure will give you some more advise.
Best wishes!