Leave fertilising to the fish; they’ll supply all that’s essential. If the plants aren’t doing well; it’s most likely due to insufficient light, or maybe they’re bunched too closely together.
If the tropical fish enthusiast is interested in experimenting, he should be careful of the fertilizer utilized. W. T. Innes recommends liquor made from pulverised sheep’s manure and shooting it into the sand about the roots by using a pippet tube. Frankly, I have never discovered it essential or desirable to fertilize, but prefer to find a trigger for the trouble, instead of introduce another element into the tank.