George no problem mate.
I feel sure you must have got some other type of grass plant, was it hard to plant? Basically tennellus looks like a mini amazon sword plant with thin leaves and its own little root system.
This is what it should look like, see the mini plantlet on the right, that is e tennellus, dont accept anything else you get as it is SO wrongly identified. As I say I only will order this plant from birstall because it's from tropica and hence correct.
Lilaeopsis novae-zelandiae often gets mistaken for e tennellus (yay spelt it right)
Easy to id by the horizontal stem and very sparse root structure. This plant is horrible to plant and in my experience I have never been able to get it to grow, it has always died without fail. I have seen people have success with it in mbuna tanks though so I suspect it needs a hard water column, my tanks are always really soft and acidic which I guess is why I am able to grow moss and tennellus so well but crap at any lilaeopsis species. It annoys me really because if it formed a thick carpet it would be a great plant.
Chrismr if you have a lot of light and your water isn't as soft as mine you may well be able to grow lilaeopsis species. However if not then tropica e tennellus is very forgiving and if you have enough light then you could try dwarf hairgrass such as eleocharis parvula, good luck trying to find this named correctly by a non tropica plant supplier I have seen it called xingu in one instance and most of the time just 'dwarf hairgrass'. Also echinodorus angustifolius is like tennellus but grows a bit taller and would look good as a midground grassy plant or to highlight stones and rocks etc depending on your aquascape. I actually think pygmy chain sword is echinodorus quadricostatus var. "magdalenesis", I'm really on the side on tropica when it comes to any plant iding you see. This plant will get you a lawn type effect but it's hard to trim and maintain although very easy to grow.
The problem is a lot of online plant retailers use contacts in asia etc, these guys seem to have different scientfic names for the plants which causes confusion with some of more unusual plants. There is so much difference of opinion I have just decided to buy the tropica catalogs and stick with those along with ADA books and Dennerle guides seem to be correct too. It's similar to trying to decide on names for mbuna or l number plecs I guess.
Sorry if I am preaching to the converted with my plant pictures btw. It's just something I find very frustrating as I just want to be able to work with the plants I read about.