We pay $15.00 for a two ounce bottle of middling fertilizer for our aquariums.
I pay $47.00 for five gallons of this for my lawn service: (big big pic)
No guarantee its clean enough to use in an aquarium, I use 3 ounces of it along side pesticide, herbicide, absorption enhancement and half pound nitrogen urea per thousand square feet. But wow, 8 cents per ounce.
Might test it on a guppy cull just to see. I blow through about three gallons of this a week, probably throw out more in drip stains on a single rinsed jug than the dose needed by a fifteen gallon every three months.
Scary. Mostly I trust Lesco. Not advising you use this tho.