Any Advice On Rainbow Fish

Iv'e decided my new 260l tank when it is cycled, will be a Rainbow tank with maybe Congo tetras if i can get away with the Ph level etc (Lfs says ok) Does anyone keep rainbows and have advice to give, i gather pristine water is a must so no slacking in the wc department. How many minimum of one variety if having a few different.

Don't you have hard water and high pH? The Thinkfish profile for Congo tetra says "although it is quite happy in harder water, over the longer term it is best kept in soft-medium water", while Seriously Fish suggests ph of 6 - 7.5.
Rainbowfish are interesting, but most do grow to a good size, though your tank is obviously big enough. I have just one Lake Kutubu fish which came with a second hand tank. I failed to find someone suitable to rehome it (I don't consider taking a fish to the LFS as rehoming, it's more like passing the buck, who knows where it may end up) and so kept it. It's more than twice the size of any other fish in the tank and dominates the others. Basically it never moves from the feeding point and explodes onto the surface as soon as the flake hits the surface. Rainbowfish are known to be greedy, care needed not to overfeed them, but apparently have narrow throats so can only swallow small food items. If mine grabs a big piece of flake, it keeps spitting it out until it breaks into pieces small enough to swallow. I've seen a Neon tetra swallow a bigger piece than the rainbow can manage.

Ooh thanks, good to know, yes Richard i do have high Ph and hard water, my Lfs is supposed to be very reputable and often tells me that certain varieties of fish are reared in UK in hard water areas so are accustomed to our water, but i will have to look into this further.Mmm Danios or Penguin Tetras, i will have to think about that too : )

The more i research rainbows the bigger they seem to get  *blink* so any suggestions, i have a 230L tank 4' x 18" x 18" i would like a school of 6 congo tetras, and wanted some banded, Lake Kutubu, and red rainbows but if i need to keep 5 of each as i have read, this seems unlikely. Is it possible to keep two of each species, and can they be all males or would a m/f pair be better? Don't want to overcrowd but it's sooo hard to choose, i like the boesmans too, but i also want some cory in the tank, oh dear 

A possiblity Sue, thanks : )

Thanks, Fishcake, oooh so many re-thinks in this fish keeping lark isn't there   

I wouldn't have Threadfin rainbows in such a large tank. They are quite shy and I reckon big rainbows, which are pretty boisterous, might be too much for them. In general, I reckon it's not a good idea to mix fish which differ too much in size, unless the smaller ones are really robust fast movers, like danios.