The co2 system is two 2 litre soda bottles with a nano glass diffuser, ive also used a bubble counter, most people will say its useless on a DIY system but i find it necessary now as it allows me to see exactly how much is being produced and with such high light there is no room for error, i built the system going by the thread on here using bulkhead fittings and pouring the boiling water in the bottle, i will get double the amount of co2 as compared to just mixing the quick way and the bubble counter proved it (2-3BPS), it also lets me know when to change the mix before any problems arise, i also use a lot of yeast (7 grams) to get it as powerful as possible but for a short amount of time as i change one bottle every 5-7 days, i do this because the lighting is so powerful and the tank so small (72W T5PC over 14Ltr) i need a massive amount of ferts and co2 to balance the light and not get algae. Im going to upgrade to pressurised and run three scapes from the one bottle as it is so much hassle constantly changing mixes when ive got other freshwater and marine tanks that demand my time. The filter is the Eden 501, rated flow is 300lph and ive added the glass inlet and outlet, mine has been OK but i very much doubt it pushes 300lph and needs cleaning fairly regular, its the only external i could find designed to sit at the same level as the tank and its only about 6 inches high so very small and unobtrusive.