I recently found a new type of clay substrate called Seramis (productname). I think it's like burnt earth but probably a different composition. The info on the website does sound promissing and as soon as i need to repot my neps ill be trying it out.
Here are some specs :
Its a mixture form different types of clay from Germany
Size of the pellets : 10% 0,5-2,0mm; 70% 2,0-4,0mm; 20% >4mm
Dryweight : 390g/liter
Wetweight : 800g/liter (waterretention >100% of the dryweight)
Amout of air when completely absorbed with water : about 50% (so enough air eventhou it holds a lot of water)
porous volume : >80%
pH : 6,2-7,3 (after 3 years still >5);
Salts (KCl) : <0,05g/100g
CaO : 0,1mg/100g
Na2O : 3mg/100g
Mg2+ : <5mg/100g
Cl- : <3mg/100g
F+ : 0,5mg/100g
So it seems to be a good candidate for neps. Ill keep you guys posted when i get a chance to test it out. For more info you can check the website :
seramisuk.co.uk