@AbbeysDad is probably on the mark here. Floating plants are rapid growing plants, and that means they need more nutrients (and light) than lower slower-growing plants. They have the aerial advantage with respect to CO2 (aquatic plants with emersed/floating leaves can uptake CO2 from the air which is about four times faster than plants having to use submersed assimilation) and being under the light that should not be an issue depending upon the intensity and spectrum. But other nutrients may be lacking, and a comprehensive liquid fertilizer (comprehensive meaning one containing all essential nutrients in the right proportions to each other) may be needed.
On this spray fertilizer, can you post a link to the brand so we can see what is in it?
Another possibility that I ran into with my so-called "Amazon" Frogbit (species Limnobium laevigatum) was what @seangee mentioned. There are other plants very similar in appearance that may be confused with Limnobium laevigatum. L. spongia is a native North American Frogbit, and Hydrocharis morsus-ranae is a European/Asian plant sometimes referred to as Common or European Frogbit. This latter is a very invasive plant that was intentionally introduced into North America via Ottawa, Canada in 1932. It has since spread quickly and by 2003 was known to occur throughout much of southeastern Ontario, southern Quebec, northern New York and Vermont and eastern Michigan. "Frogbit" is classified in several states including California and Washington as a noxious weed. It is likely that some aquarium plants are in fact not L. laevigatum but one of the other two. I discovered that my "Frogbit" was the temperate species when it flowered; flowers are often the only way (aside from DNA) to differentiate species when it comes to plants.
On this spray fertilizer, can you post a link to the brand so we can see what is in it?
Another possibility that I ran into with my so-called "Amazon" Frogbit (species Limnobium laevigatum) was what @seangee mentioned. There are other plants very similar in appearance that may be confused with Limnobium laevigatum. L. spongia is a native North American Frogbit, and Hydrocharis morsus-ranae is a European/Asian plant sometimes referred to as Common or European Frogbit. This latter is a very invasive plant that was intentionally introduced into North America via Ottawa, Canada in 1932. It has since spread quickly and by 2003 was known to occur throughout much of southeastern Ontario, southern Quebec, northern New York and Vermont and eastern Michigan. "Frogbit" is classified in several states including California and Washington as a noxious weed. It is likely that some aquarium plants are in fact not L. laevigatum but one of the other two. I discovered that my "Frogbit" was the temperate species when it flowered; flowers are often the only way (aside from DNA) to differentiate species when it comes to plants.
