The best of the Oil Dri sorts of products is Safe T Sorb. So far I have only found it available at Tractor Supply.
Kitty Litter may work for some, but different kinds may fall apart, cloud the water and so on.
The Oil Dri products are better, do some more research. Many are white or off white. That is not much of an issue in a grow out tank, but if you move those plants to a tank with different substrate and some of the Oil Dri sticks to the roots the whiter material of most Oil Dri products would not work too well.
Safe T Sorb seems the best of them all. Pretty good color too.
A related material is used in sports fields, and may be cheaper if you are not near a Tractor Supply. For me it is about twice the price, but the saving in gas makes it half the price of going to Tractor Supply. It is sold at irrigation stores like Ewing or John Deere. It is called Turface Pro League. It comes in several colors. The redder one is too red, but the other colors are fairly subtle. I started using Soil Master Select, Charcoal and it works pretty well, and I like the color. Unfortunately SMS is not available any more. Turface is about the same, though.
All of these materials are relatively lightweight, so some plants might need a rock on them to hold them down until they root.
They are all high cationic exchange capacity.
Turface and SMS will remove the carbonates from the water. I have stopped that with coral sand, mixing something like 50% Turface with 50% coral sand. I use that for a Lake Tanganyika tank. You could also mix in oyster shell grit (sold for caged birds like Budgies) or limestone sand or very fine gravel.