You're looking for treacle in U.K.
I use 1TBS per gallon and start using it one month into flowering. It works.
It's thick and you'll need to heat it, then add it to the water. Put a little water in a pan, add TB treacle, heat, add to remainder of water.
I advise using all you make at any one time. Stored mixed, in jugs, mine seems to ferment and stink/reek.