Nitrates help

[Chris82]

65 gallon. fluval filter,led light. live rock mixed reef.
i have been having high nitrate problem for ever... i bought system used 2 years ago and think its probably 6 years old now.
i unfortunatly did not know better and used the used sand. i have been told this was a mistake and have now over a period of time got 80 percent of it vacumed out. but i still have issues.

has anyone heard of live rock becoming saturated over time.?

any help on this would be apreciated.
cheers chris