ok,thanks for your help.
i`ve just been down the lfs and come back with a juwel rekord 600.
sand is washed and in...as are the plants.bloke at the shop says run it for a week,and then put some sponge from my main filter in the tank along with 2 cory.
then add 2 more fish per week.
anyone care to comment on this?
Running the tank sans fish for the week allows the water to "age" - never a bad thing when setting up a brand new tank with new sand etc (if there is any residue from tank manufacture or sand, time is provided for these to dissipate, certainly the "smell" changes during that week), your lfs is being conservative. If you add sensitive fish or inverts to a tank set up yesterday, even with a sponge filter taken from another tank, you will observe signs of stress.
The shop bloke suggested adding the sponge from your main tank at the same time as the first 2 cory's so not sure why so many posters are implying that the bacteria will "starve" - again the shop is being conservative, even if you only have a few bacteria in that sponge, following the shop recommendations mean the fish will not be stressed, as time is always given for the N-cycle bacteria population to increase along with demand.
That first week also allows time for the plants to establish; note if tank is heavily planted & plants are actively growing (especially "fast" growers) when you add fish, it's possible that plants will consume any ammonia as its produced, so if you remove plants at some point or have significant plant loss/death, monitor for ammonia/nitrites & perform daily water changes.
As always, much depends on the sort of fish, the density of fish population, the water pH & temp ....
If you're able to monitor the tank & perform water changes as needed, then go ahead & add everything all in one go - this may work out very well or you may have some fish stress re ammonia/nitrite spikes - the shop is being conservative but is giving a formula that has almost zero chance of fish stress).
Even if you do add the sponge from your main tank & leave it some days without "food" from fish, those bacteria will be fine - they are not rapidly growing/metabolizing bacteria (as I recall the "doubling time" is ~ 72hours (pH ~ 7.0 & temp ~ 76F) ... it's been a long time since I read the papers) so they may lag a bit but none will "die", further any leaf melt from the plants will feed the N-cycle filter bacteria just fine.
What you never want to do is leave these type of bacteria submerged with no water movement for more than an hour or so, these bacteria are very sensitive to oxygen levels which are provided by the moving water, if you ever need to "store" your N-cycle bacteria, just remove from the system, rinse any debris (which feeds the other types of bacteria that also populate your filter), & keep damp, eg in plastic bags with a bit of water & lots of air, or in a canister filter with a couple cm's of water at the bottom & closed at the top except for the open inlet/outlet.
(obviously use tank water to treated tap)
Taking a portion of media big enough to cope with six fish
I'm quite curious now you determine this amount of media
I though maybe you had some tested formula worked out (or were plating out bacteria & doing counts)