u really should do 50% or more on wc doing only 33% is pointless.
whole point of wc is to remove the old water with high ammonia &
nitrites and add new water to dilute the water remaining in the tank
to maintain a good water parameter. doing such a low amount every
week defeats the purpose of wc unless your doing 33% 2-3x a week.
and as i said stop over feeding. just stopping over feeding will give you
better water parameters and the need to "filter" out excess food & wastes
that causes the water to pollute.