What is the best substrate for cichlids sand, gravel, crushed coral

I have a emperor 400 filter, and will get eggcrate for the glass' protection..

What's best for cichlids. sand, gravel or crushed coral?

I should mention they are mbunas, lake malawi.. yelow lab, kenyi, and electric blue ahli

I'd recommend any sand but not too fine sand because fine sand could damange your emperor 400 (the spinning device).

I've had luck with pool filter sand, make sure it's 100% silica. If your local tap water is lower in PH, i'd suggest add crushed coral because crushed coral will pull your ph and hardness up. Mbunas like ph between 7.9 to 8.5. Pool filter sand don't build a posion gas on the bottom. Play sand will build a posion gas but it can be avoided by stirring your sand to release the gas once a month.

Type of sand is really your own personal preferences. I've found gravel harder to clean with Mbunas. Mbunas prefers sand and i've noticed big differences between Gravel and Sand with them that's why i switched to sand.

you would need to add another hang on back filter. One emperor gives you 400 gallon per hour so you'd like to have another filter to make about 10times over per hour. I'd recommend Aquaclear, since you can make it solo for mechanical filtration. Just put the sponges on the bottom then in the middle add more 100% poly floss can be found in you local fish store then discard carbon and ammonia bags, buy Seachem Matrix and put some in a mesh bag and lay on the top of floss. It will make your water very clean and clear. Since Seachem Matrix can be used repeatively and does not need to replace every month. Just rinse the sponges and the Seachem Matrix in a pail of tank water so you don't kill baterica. Just remove the dirty floss out and put new ones in.