Brian wrote:
I have a large tank with a light fish load. My nitrates are around
10PPM. Do you need to do a water change with such low nitrates?

Water changes not only lower the nitrAte level within the tank, but
also the DOC (Dissolved Organic Compound) level. DOCs are the uneaten
foods and fish waste within the tank that has decomposes/dissolved and
that passes right through the filter. A weekly 20% (or more) water
change is needed to keep the DOC level from accumulating over time.
Without the water changes, the water problems because of the DOC
build-up slowly deteriorates and the fish start to suffer from stress.
The build-up of DOCs also create conditions that encourage disease,
parasites and opportunistic bacteria.............
Frank (FB)