[Higher Thinking]

It all depends on your desired substrate depth. The 9l bags are surprisingly large when filling footprints. I think I used a bit more than one for my 20 longs, but I can't remember for sure. I had some decent depth to them as well because I made multiple tiers. So to get back to your original question, yes, you could use one bag to fill the footprint of the 17g.

 

[Discusdude7]

It all depends on your desired substrate depth. The 9l bags are surprisingly large when filling footprints. I think I used a bit more than one for my 20 longs, but I can't remember for sure. I had some decent depth to them as well because I made multiple tiers. So to get back to your original question, yes, you could use one bag to fill the footprint of the 17g.

Would one bag fill it to a depth of 2 (or 3) inches?

 

[talontsiawd]

One bag is about perfect for a "regular" tank with just a gradual slope. Just measured mine and the front is about 1.5 inch, the back is around 2.75 inch. Now if you want a more significant slope, or are adding slopes for any hard scape, you will need more. Though one bag works, it's the minimum you would want for that tank size.