02-02-2011, 05:34 PM
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I've used two most recently, the Flourish and the Nutrafin Plant-Gro sticks. The latter certainly work, and they are much less expensive because they last for a year. I inserted Flourish tabs last week for the first time, I couldn't find the Nutrafin anywhere locally so decided to try the Flourish before ordering online. Flourish says to replace every 2-3 months, so long-term they are certainly more expensive.
As for the other part of your question, what plants need them: substrate-rooted plants (swords, crypts, vallisneria, aponogeton, sagitaria, etc) will obviously benefit most. But, these can all be grown with only liquid fertilization provided it is complete.
Swords (Echinodorus) are heavy feeders. I did an experiment two years ago, inserting a Plant-Gro stick next to a couple swords and leaving others of the same species without. After a couple months, the swords with the sticks were definitely larger, and when I pulled the plants out (moved the tank) the root systems were much more extensive too. I have also had good growth with only Flourish Comprehensive liquid, though perhaps not as strong. If you don't mind the cost, i wold use the substrate fert sticks/tabs with large sword plants.
I suspect the latter point is the source behind the comment mentioned by Gina. My experiences over 15 years clearly show that swords can be kept quite healthy with only weekly liquid fertilization, but adding a substrate fert does increase growth. By the way, twice weekly liquid (Flourish Comprehensive) was also necessary notwithstanding the substrate fert, in order to keep the swords lush and green. As I mentioned, they are very heavy feeders.
Hope this is of some benefit.