Agreed, I used JBL AquaBasis+ as a base in my 300L tank and got it from ZooPlus.
Plants seem to love it when they get their roots into it, but do make sure that the tank is as empty and dry as you can get it before adding it, as it turns into a rather horrible bubbley pink soup as soon as it touches water - lol
Thier website can be a bit frustrating to navigate so here is the direct link:
[URL="http
/www.zooplus.co.uk/shop/fish/aquatic...materials/14366"]http
/www.zooplus.co.uk/shop/fish/aquatic...materials/14366[/URL]
It doesn't contain N&P but if you are adding those to the water column anyway then the clay in the AquaBasis is supposed to be quite good at storing and releasing these.