After BL sugested a denitrator i thought about this idea! Not wanting the problems of winding airline and all that! I thought of using some of that polycarbonate sheeting (you know the stuff some greenhouses are made of - the sheet that is made of lots of little "boxes" of a sufficient size to get about 50 foot of tubing (can make it multiple thicknesses to save on space). basically i will make a notch in the top of the first section, the bottom of the next, then top and so on.... in other words the water must flow down one column and up the next where it will go over the top into the column next to that and so on... if i am to use multiple thicknesses then the last notch will be into the side wall so water can flow into the "next section". i was then thinking of using the last few columns as an oxygenating zone by adding an airline. the water input will be at the top of the first column, with the exit about 2 inches up in the last column ( hopefully keeps water and humidity up if there is ever a prolonged power cut) obviously the unit must be airtight for it to work so off cuts will be used to be the top and bottom which will either be siliconed or plastic welded into place. i was also thinking of having the output of greater diameter than the input to alow for crud to exit the unit (have heard that coil types can clog after a year or two). using an airline valve on the out put i can regulate flow to about a drop a second. and hopefully hey presto! Has someone made something like this? will it work? anyone see any problems? Do denitrators need initial feeding (such as a couple of grains of sugar) to get stated? Happy to hear comments and criticism.