BOTH! Root tabs for root feeding plants like Sword plants and Crypts, etc. Liquid ferts for stem plants and ferns like Anubias, Java Fern, Ludiwigias, Rotalas, Hygrophilias, etc.
Please research macro & micro ferts and what each is for. No need to be nervous about using ferts made for aquariums. Where people get into trouble is trying to use land based ferts without carefully researching. OS.