I used to keep freshwater fish, and regularly used the water from cleaning the tanks to water non-food plants. I have no real idea if they benefited or not. I was never comfortable using that water for vegetables because of: a) the conditioners used to treat the water; and b) the risk of parasites/diseases from the fish.

With a saltwater tank, I'd also be concerned about the increased salt in our already salty water and soil.

What I'm referring to doesn't involve any water from the aquarium, so there's no salt involved (a salinity test for specific gravity proved this) . . . this stuff is the product of a mechanical protein skimmer which, using fine bubbles, creates foam (literally seafoam) which pops the protein waste solids up and into a catch. I then take those solids, like the consistency of natural peanut butter, and dilute them down with RO water, maybe around a couple tablespoons to a 1/2 gallon of water. Probably could go to a gallon and still be good.

I never add anything to my aquarium besides sodium carbonate, magnesium, and sodium chloride, so as far as conditioners, chemicals, etc..there are none. And about parasites...very unlikely once it's diluted down into fresh water. I'm sure though, that there are some good pro-biotics in there.

This stuff smells horrible, and as we all know, anything that smells horrible has to be good for an organic garden!

Does anybody know what "fish emulsion" that you buy in the store is made of? I'm curious if it's this very thing.

Oh duh. I've run across discussions of protein skimmers with saltwater tanks, but didn't make the connection with what you're talking about until you explained it. 'Scuse the false ring :)

"Fish emulsion" is made from fish flesh ...

I can't think of any reason you can't use it on plants - it will be decomposed into nitrogen the plants can use.