i got the 60-P 17g, will one 9l bag be enough? I want to make some slopes and hills.

Here's a link to the Angelfins site calculator for Aquasoil amount required given particular tanks and depth desired.

Aqua Soil

While we're used to seeing substrate in bags measured by weight, and a bag measured by volume looks weird, it's actually more straightforward. All you have to do is figure out the volume you need in the tank in cubic inches, then divide by 61 to get liters.

Whereas with a bag measured in pounds, you *need* a calculator because without prior knowledge, there's no way to tell how much volume is actually in that 15 pounds.

It's tougher when you want to add irregular slopes, but that's something that nobody else can really help with.

3" substrate in a 60P would need at least 13L. I just ordered 18L with my new ADA 60P just to be safe since I also want hills.