As it is pertinent to this discussion, I will post some data comparing Osmocote and Flourish Tabs. From the respective websites, these products contain
Nitrogen (Osmocote 15%, Flourish Tabs 0.28%)
Phosphate (Osmocote 9%, FT 0.17%).
Second, there is no calcium in Osmocote, whereas FT are 14.9% calcium. Now, I admit that with moderately hard or harder water calcium is unlikely to be an issue. But it is still more important, and less detrimental overall, than nitrogen and phosphate in such incredibly high numbers. Insufficient nitrogen should not be a problem in most fish tanks as the ammonia/ammonium produced by fish respiration and the breakdown of organics by bacteria will be sufficient, and phosphate present in fish foods is more than sufficient. In high tech set-ups, using diffused CO2 and mega light, these obviously may need boosting, but not to the levels in Osmocote regardless.
Hope this helps others understand why so many of us are against terrestrial plant fertilizer products.