thanks palThe "general" rule of thumb is 1 lb of substrate for 1" depth for every gallon.
1" substrate in 20 gallon tank = 20 lbs of substrate
2" substrate in 20 gallon tank = 40 lbs of substrate
so 19l = 5 US Gallons (roughly) which means you would need 5 lbs of substrate to get a 1" base or 2.26 kg. So your 2kg bag should give you the right amount for a 1" layer.
cheers for the input matey... its only a few extra ££ for 4kg of shrimp stratum over the 2kg of plant stratum so i'll do it that way roundYou can't base this on weight. Fluval Stratum is extremely light-weight.
Additionally, Fluval Shrimp Stratum (same as Plant Stratum, just smaller grain size) would be a better scale for your tank.
You'll want to get at least 4kg. May have a bit left over but it's better than not having enough.