If carbon doesn't clear it (my assumption since most stock cartriges have some carbon), and all the fish appear healthy, no overfeeding (even though feeding every other day can still be too much depending on how much you feed), no discoloration and no visible algae anywhere else in the picture, test kit is in normal range and tank is done cycling (please give numbers as well including ph, "normal" differs person to person) - all this combined leaves not a whole lot other than maybe high TDS. Possible your source water is already high in TDS (e.g. very hard alkaline water). Try a big waterchange with RO water and see if that clears it up.
This is not a good idea, Duckie. A large-scale water change with RO water will likely cause osmotic shock to the fish.
To the OP...RO is short for reverse osmosis, a type of filtration that forces water through the pores of a semi-permeable membrane to remove virtually all total dissolved solids, down to bacteria, from the water; lowering the total dissolved solids to something approaching distilled water, depending on the efficiency of the RO system and pore size of the membrane.
Water can cloud for several reasons, typically an algae bloom (all of which are not green). I'd keep up the maintenance routine, including heavy gravel vacs weekly along with minimum 50% weekly partials. You might try decreasing your photoperiod; the amount of time a day your lights are on, by a couple hours. Be patient. Also, persistent cloudiness can sometimes be reduced by putting some filter floss in your HOB filter(s).
Mark
