Don't use rocks or sand; just worry that the pot has NICE BIG DRAIN HOLES! That's what your plants want the most. And make sure the soil is very light. I'd add some extra perlite when you mix it up, to help it drain better.
If you don't have a pH meter, I hate to sound like a spokesperson for Canna and Botanicare, but the Canna Terra and Botanicare Pure Blend nute systems are buffered so that you don't have to adjust the pH as carefully. Be sure to flush out all that miracle grow chemmy fert though, because your plants look locked out already. I'd go with a plain non-fertilized potting soil, bagged compost, or promix cut with perlite by up to 30%.