DJJ624
Water changes are truely one of the hardest things to give advise on.
Each of our tanks are unique - and what works for one person may not work so well for another.
There are just way too many variables involved.
In my opinion, the very best advise one should consider, would be to try out different water change schedules/amounts on your own tank - and see what works the best.
I do favor water changes over not doing them at all, but the actual amount and frequency will be different for each of us.
If you're planning on doing a 5% per week on your 55, for general maintenance to freshen up the tankwater .... I think that's fine.
If you're planning on doing this same 5% per week for nitrate reduction or other corrective measures - I don't think it's enough to make much of a dent.
You kind of need to ask yourself - "why am I doing this water change today?"
Try it out - change it around a little - notice the condition and appearance of your tank/creatures - watch your test kit results ..... and make some changes if necessary.
Eventually you'll hit on the right amount and frequency for your individual tank set up.