flood and drain

greets all,

i am looking to move into hydro- esp flood and drain, after 25 years of outdoor and 15 years(sog, scrog etc)indoor. im using to start with, a 4 pot system with system reservoir and header reservoir as they are on special at my local grow store, i got air stones for both res, water heater etc etc... using hydroton clay balls. my question is, using hydroton's in pots(approx 16 litre) how often should i look to be flooding and for how long? also how often should i change my res water?? after a week or so? whats a good determinant to know when to change res water? im also using growzilla and budzilla for the cycle... ive seen in other posts to flood around 3x per day for about 15 mins each in the light cycle... just wanted to ask regarding the size pots i am using and the fact im using clay balls as my medium. also to clarify- i dont flood at all in light off cycle right?? one more question, im using 4 pots and know i can ugrade to another 2 pots(total=6 pots) do you think i could upgrade a further 2 pots using the same size res?? (total=8 pots).

thanks all

ok.. having sorted the questions above... i was wandering if i could get some of your advice on the fact that this system uses 2 reservoirs. i live in new zealand so im looking at this locally made kit but what im curious about is it has 2 reservoirs... one "header" reservoir and one "main" reservoir.. the header sits atop the main... is connected by 19 ml tubing to the main/lower res, which connects to a ball- cock valve unit within the main... im just wandering what the advantages are of the 2 res's.. and is it necessary? would i be better to just use one reservoir? the main/lower res houses the water pump-which feeds the feedline to the 4 pots, a water heater, an air stone, ball-cock valve and nutrient solution. the header/upper contains only water and a 2nd air stone. it is also considered a re-circulating system as opposed to a run off. any advice would be welcome. here is an image and details of the system: http://sog.shopau.biz/catalog/product_info.php?cPath=8&products_id=363

being a re-circulating system im unsure about the need for the upper/header res... if it were a run off system i might see the need for the 2nd res to re-adjust water levels.. or maybe in flowering stage? when the plants might drink more liquid?? im unsure about this... any advice or experience with this would be greatly welcomed

regards