new to marine tanks

Question
QUESTION: hi i have just bought a full 3ft marine setup its been running for 2 years.lots of coral and live rock in but i have just noticed a brown tinge to the gravel and unsure what it is please could you help and could it be harmful.thanks

ANSWER: Hey Steve,
Not harmful, but a sign that the water quality needs help. Thats either an algae or a cyanobacteria. Both of which thrive in systems with over extended photo(lighting) periods and nutrient(detritus/decay/nitrates) rich waters. Test your water quality. See where you stand there. When you buy a existing system and move it, there is a disruption of the biological filter(the bacteria) and it can take a while for it to catch back up population wise. Cut your lighting back to no more than 9 or 10 hours a day, and reduce amount of food given at feedings. You should also use a substrate vac to physically remove as much as possible and change about 25% of the water. Have you done a saltwater change before?

---------- FOLLOW-UP ----------

QUESTION: Thanks very much for reply. When we the moved the tank we lost some water so we took a water sample to the pet shop and he said salt level was bang on and the nitrite level was great but the another level was out so he gave us some rowa phos for that. Is a substrate vac the same as a gravel cleaner for a tropical tank.We did top the water up yesterday we're just going to test the water now. Sorry for the silly questions i just really want to get it right thanks very much for your help.

Answer
Hey Steve,
No problem! And no questions are silly when youre trying to learn to do something new and the right way to do it.
Yes a substrate vac is the exact same as your gravel cleaner. Now with a saltwater aquarium, you dont want to go more than half the depth of the substrate when cleaning. Going to deeply can kill too many of the bacterial colonies that make up your biological filter. I would get the water chemistry(ammonia,nitrite,nitrate,pH,phosphates,calcium) corrected/adjusted by doing water changes. 25% to 30% every 2 or 3 days. It's just a better way to get the system and the biological filter back on track and strong, rather than using additives that "trap" and "neutralize" the toxins in your water. If you hav pH fluctuations, they become active and toxic again. But thats just my opinion.
Good luck! And let me know if you have any more questions.