I've been wondering about this myself. This stuff is way cheaper than API Root Tabs or Flourish. Any advice out there?
API also sells a pond plant food tablet product that's much cheaper than what they market for aquariums. Is there a difference?
It has a much higher NPK ratio than API and Flourish. I'm not sure how much that will affect water parameters. What I would be concerned about is the source of nitrogen in the Pondcare product. Ammoniacal nitrogen is 4.86% from ammonium phosphate. Unless you have acidic water it's likely to cause an algae bloom with that much ammonia.
I have some of this, but my 9oz package contains, Sodium Molybdate. Like Zorfox mentioned, it's got a higher concentration of nutrients.
If you add it to your tank, it will dissolve into a cloudy mess like shredded wheat nugget in a bowl of milk & possibly kill off all your livestock. It's designed more for pond plants that require HEAVY fertilizers that are kept in pots & other containers.