Yeah, off-the-shelf aquarium fertilizers are formulated with much more conservative nutrient levels so that everyone can use at recommended dosages without affecting sensitive livestock or requiring consistent large weekly water changes. They are designed to be as easy to use as possible.
Those bottled fertilizers would definitely look alot less value for money compared to dry ferts, whereby EI dosing advocates way higher levels of fertilizers dosed on a daily basis, and then have to flush away the excess every week with large 50% water changes, that level of constant maintenance is meant for the small but avid group of dedicated planted tank keepers... not exactly an attractive proposition for the majority of casual (or lazy) planted tank keepers/aquarists who have a tendency to skip tank maintenance and water changes whenever they can.
I guess most LFS cater to the aforementioned casual aquarist, and selling bottled products regularly to customers sustains their business... unlike selling dry ferts which a person can use for years and years, like that no repeat sales.
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