Is my question too strange? Any suggestion is appreciated.

Thanks again.

Anyway, I am trying the aquatic iron supplement on my plants now. Hopefully they will like it.

memder, I would make quite sure that the plant was suffering from an iron deficiency; in my experience, iron deficiency shows up because the plant cannot take up the iron in the soil. I would correct the cause or use a product for foliar uptake, whichever is less expensive.
My intended use must always be covered in the labelling of the product.

You're from Pa.? Then you are probably growing in containers. Are you atually seeing a chlorosis that makes you want to add iron? If not houseplant fertilizer with miro nutrients should be all you need. Also, if your soil isn't acid enough the plant can't absorb the iron. The iron that I've used in the past was "chelated" but I don't know what that means. Also, if your foliage is pale then it may just be that you need to repot. Anita

I should think an iron deficiency quite rare unless you are growing in a artificial medium i.e. not soil.

As ronalawn82 implied it is more likely an iron availability problem rather than an iron deficiency problem. One way this is corrected is with a "chelate" as suggested.

In any event I cannot imagine how iron supplements for animals like acquarium food or human vitamines would work. These might indeed work fine. I just can't visualise the chemical mechanisms

BTW, what are your symptoms. Are you seeing chlorosis? If so this could be caused by poor drainage, damaged roots, magnesium or zinc deficiencies or other things.

Milorganite is 4% iron. Your $10 will buy a 36 lb. bag that smells like crap.

Here is a link that might be useful: Milorganite