if you are using a 40 gallon long refugium you can use mangrove pods to suck up nitrates and they can be trimmed to dwarf them small. I use mangrove pods in my hardwater freshwater sumps/filter and they are thriving.
I pick up my pods, that wash way up the beach shore and are near dryed up & I take them home and revive the pods in hard tap water.
I see pods bieng sold all the time on ebay & CL.
if this is not an uption there are many plants that can do well in hard water such as hornwort and grow fast in low light,
Last edited by JoeGREEEN; 12-08-2012 at 04:16 PM.