IMHO Nitrates is the bi-product of the cycle produced from bacteria breaking down waste, and it will remain and or increase in the aquarium unless you take steps to remove it. The removal can be done through water changes, skimmers, algae scrubber or macro algae, binding with a carbon source and skimming. Nitrate doesn't leach out of rocks although the die off of organisms on the rock can produce nitrates. Live rock die off would have a greater chance at producing nitrates then anything dried up and dead on dry rock. When nitrate is produced on the surface of media such as bio-balls, dirty filter socks or pads it mixes into the entire water column, and if not manually removed by water changes it has to find its way to the places where it may be reduced inside of the rock, deep sand bed, or low oxygen bacteria area and is converted into N2, and the N2 to into the air.
1. Water changes-- Don't use tap water. Use pure 0 TDS RO/DI water.
2. Remove all dead matter from the live rock before placed into the tank or cycle the rock first in a tub.
3. Don't be lazy - Clean all mechanical filters. Change filter socks sponges and pads every 3 to 4 days.
IMHO mechanical filtration is a great way to remove suspended waste from the aquarium before it breaks down and can prevent nitrates before they happen. It is far better to export uneaten food and waste then let it settle somewhere in the tank or sump and produce waste. BUT you have to clean and or replace the filter media before it does start to break down or it will do more harm then good. That is why some lazy people call such filters "nitrate factories"
4.Blow off the rocks during maintenance on the tank. use a mechanical filter to remove the suspended crap or it will just settle somewhere else. Remember to change out the filter pads.
5. feed less, spot feed. Shut down the flow and feed only what the fish will eat. Don't let the food go everywhere. spot feed if needed.
6. Go +1 on skimmer
7 Let the bacteria do the job---Use a carbon source with skimming and or bio pellet reactor.
8. Algae can be your friend. Add algae scrubber and or macro algae to the sump.
9. Although not my favorite fix all, deep sand beds have been known to reduce nitrates. Not debating good or bad.