Hi Alice,

Thank you for your inquiry.  To better help you we will need a little more information such as size of the tank and water parameters (pH, salinity, temp, ammonia, nitrite, nitrate, phosphate, etc...) with actual numbers.

To better help with this problem, please either visit our online forum or send us an email directly to customercare@marinedepot.com.

I have linked our articles below that might help in the mean time (there are many that hopefully will help answer some of your questions):

http://kb.marinedepot.com/default.aspx?cNode=4O3V2M

Liverock for the most part should be fine for many years in the tank assuming there are not "issues".  If you have problems with high nitrates and/or phosphates, those can sometimes become trapped inside the rock and can help feed the algae.  Most people though will keep the same rock for many year, some others prefer to change out some of the rock once a year.

Keith M.

Marine Depot Customer Service