Sounds like it is time to start the hatchery. When offering BBS at first introduce small amounts by squirting some over the parents and allow the BBS to float down to the fry. I like to use a syringe with a bit of rigid tubing attached to the syringe with a bit of airline tubing. You can use the syringe to suck up any amount of BBS. It will take the fry a few days to go after the BBS.
Pat