I have a 20gal tank existing, and i just picked up another 20 for a sump/refug....I often hear that most systems that have a mech filteration system cause nitrates>>what kind of system could be set up with the other 20 that is good biological filteration(nitrate/phosphate reducing) im also thinking of building a good skimmer from some design on the net.............I guess this is the deal -- Im asking for ideas on what i got.. I have a 2year old 20 gal High with coral/LR/fish/DSB and PC lighting. I now got a stand to hold this tank and another 20 high underneath it for growing macro for nutrient export how best can i set this system up?? How can i make the best natural filteration?? Ideas on this new set up please