Something similar happened to me. I decided I wanted to put some plants in my 40 gal. Tanganyikan. I bought a mess of plants, and a big bag of flourite because, "...hmm I think I'll get rid of the aragonite and put this in." Then I got the stuff home and wondered what the heck I was thinking! Ok... I have an empty 10. I'll put the flourite in there with all of the plants and be done with it. I rinsed and rinsed the flourite. Finally put it in the 10 gal., filled the tank, and after a week, it was still not settled. I finally planted the plants in the sand in my Tanganyikan tank, emptied the 10 of water and stored it. Last week I picked up a 2 1/2 gal. on sale for 8 bucks with the lid, and I put in some of the flourite, a betta, and a lot of small plants. This tank is on my desk and it looks great. Now that the weather is warmer, I'm going to get that flourite outside and rinse the living daylights out of it with the garden hose. Then, I'm going to use the 10 as a planted tank, with the flourite, to raise shrimp as treats for my other fish.
Small tanks and sponge filters are cheap, so you might want to think about doing something similar to what I did. If you buy flourite new, its rather expensive and a real son of a gun to get rinsed, so you are already two steps ahead of the game.
Steve