I now have 12 2-4" mbunas in a 188 liter tank, 30 liter overhead SUMP, 3-4" thick coral gravel, ugf/plenum with a 4" lift tube as the doc recommends, 2 BCBs in the top SUMP with oil-dri and laterite. 0 ammonia 0 nitrite and 40/80 ppm nitrate. My tap water has high nitrates so I tried using bottled drinking water and was shocked to discover it has high nitrites so switched back to tap water! Waiting for the nitrate eating "bugs" to kick in now.