First Time NFT.. Need Advice

Hey dudes. I wanted to ask some questions. I have completed a few successful outdoor grows. I wanna switch to hydro growing and have decided on a PVC pipe nft system. So its going to be 20 plant system with 6 inch pipe. I have a 185gph pump but i was wondering how big i need the water tank. P.S. I am planning to grow with CFL's. I have 3x105W 6400K and 6x60W 2700K lamps. I am planning to add more. Can you give me any ideas? Thanks, smoke in peace

Edit: The room is 8x5.5x4.5 and is newly painted white.

And i am going to use Canna Aqua series with rhiztonic and cannazym.

it depends on how big you want to grow your plants, but as a general rule you can get away with as little as 5 liters per plant if the plants are small, (no or very little veg time), however this would require you to top up the tank every day so 10 liters per plant would give you more time between fillings, and also less shift in the ph and cf values, when the water level lowers, the cf and ph will change, and when you fill it up again the ph and cf will change, so its obviously better to use as large a resiviour as possible in your situation to avoid this