Having that size tank changes a whole lot of things.
A breeding pair of Jaguar cichlids will completely take over a tank smaller than 180g and are extremely aggressive when breeding. Not to mention they are going to outgrow that tank, males easily reach 40cm (over a ft in length), while females stay just under a ft.
The issue is not about substrate here, it is about these fish now being incompatible with the size of tank you have for them. If you are going to keep them, which I can almost guarantee will cause major issues if they are housed with anything else, then you would be looking at a sand substrate.
Something to bare in mind as well, the female will produce some 400-500 eggs when she spawns and if not kept in a separate tank when spawning, these fish WILL chase anything which comes near them, they can quite easily kill off an entire tank.