Looking at the rest of the tank it could look so much better
Sand is cool, but may be a bit of a problem in a tank that size. Mainly for washing it, but you could filter out the fine particles in your tank. Something like river sand because its varied particle size and you can get it from soils aint soils or similar.
Otherwise, go some kind of gravel thats the same colours. Depends on your taste, but I think black would be best (especially as you said they are night fish). Some gravel from a soil place would probably be more cost effective. Remember it looks different wet though (get some samples, wash them and chuck them in your tank in patches to see how it looks.
The rest of the layout. I recon you should get some large driftwood pieces. The bigger the better as it will look better in the tank (especially compared to the small pieces dotted around the tank
). Lie them somewhat diagonally. Something that would look ridiculously awesome would be to get a tree root the height of your tank, and place it in one corner by cutting off everything but a corner of roots. Perhaps there are some treestumps around there that you can use (I have no idea though). You could even split the tree and put half up against the background, and a quarter piece in the corner. Otherwise, maybe some large pieces arranged randomly (to provide shelter). Mangrove type roots would look really cool at the back of the tank and provide hiding spots for fish, but i dont know how easy it would be to implement.
As for rocks, try putting in some large ones. The bigger the better (as long as you can lift them), but make sure you can put them in the tank without dropping them. Perhaps some kind of sling system just cause of the difficulties in leaning over and into the tank. Then cluster the rocks on one side and scatter some smaller ones throughout the tank. Put the rocks onto 'eggcrate' or similar material (bunnings have plastic 300mm drain covers that work well) to distribute the load and prevent point sources. The glass can support heavy rocks (as long as the stand doesnt let the glass flex, but glass cant support point loads, like a pointy bit of a rock, or a grain of sand stuck between the rock and the glass. Then fill the gravel/sand in after the rocks so they're bedded in a bit.
Some plants would be cool, but might not really be feasable.
Perhaps you could simulate some kind of riverine environment in your tank? Might need powerheads, then shape the sand in a meandering shape devoid of rocks, then use coarser sand and rocks outside of that.
Though the best way to setup your tank is to look at other peoples tanks. Try browsing through the tank galleries at cichlid-forum.com. Many zoos also have very nicely setup natural looking tanks. Also, perhaps look at underwater shots of where your fish are from for ideas.
