Both fish (Parrot and FH) that you're keeping now are tough as nails!! Not many other fish are as tough as the fishes u're keeping now. If you try doing 100% water change on many other types of fish (without aged water), u're likely to get dead or sick fish. Trying doing 100% water change on fish like Rummy nose Tetras. I'd bet they belly up with the sudden change in water chemistry.

There's no point in doing 100% water changes anyway so why spend the extra time (and risk your fish). 50% a week is plenty (and u never have to remove the fish from the tank!).