Hi Tizer, I used your idea with the cat litter, I'm new to all this fish keeping business and want to have plants as well as fish, I heard on a few other forums this cat litter is very good (other than the washing of it) and over time gets better at holding plants in (3-4 weeks) as it gets heavier.
I only have a small tank (105 litres) but, I'm saving for something bigger (330 litres) and need to get in to the fish keeping business (too excited to wait)
Great tank by the way and cheers for your inspirational ideas!!
Here's how my tank turned out 24 hours after putting the washed cat litter in.