Agree. Many of the plant fertilizer preparations are insufficient as they only contain certain nutrients, especially those that may be less expensive to buy. But Flourish Comprehensive Supplement
has everything, and the very small dosage means it will last for months so long-term is is much less expensive plus it does a better job.
Another equally good is Brightwell Aquatics' FlorinMulti
. Similar low dose, and a complete fertilizer.
Whichever you get, make sure it is exactly the product named, since both manufacturers make several products in their respective lines.