Possibly you need to ask yourself if you really need more fertiliser. Are there any signs? Philodendrons and Epipremnums being epiphytes don't need a lot of fertiliser so what's in the fish water is probably enough. You risk getting it in your water and promoting algal blooms. There may be a problem with those plant species being too wet. Our local native Epipremnum amplissimus does normally grow with it's roots submerged in water (in creeks) but some of the others just like damp with plenty of air. That's just my views on it.
