I “roll my own”.
I use common clay (it has extra iron), crush it to a powder,
then use pre mixed macros & micros to wet it.
Roll it into marble sized balls and let dry.
Push em into the substrate once a week.
If you’re careful, the water does not cloud up.
Works great and a lot more inexpensive than store bought ones.
When I gravel vac later, the excess clay comes out.