for african cichlids: slate vs lava rock

I avoid rough rocks because they inevitably end up scraping up fish. In my 150 I have one structure that is slate stacked with PVC T-connectors spacing them out. Smooth rocks are more natural to the biotope anyways (Lake Malawi at least, which I am assuming).

I agree with reptileguy the smoother the better, but if I had to pick between the 2, and this is my personal preference I'd go with lava rock rather than slate (no personal experience with it, I use river/cobble stones in mine, but from what I've seen alot of malawi tanks have lava piles in them and fish seem to be doing fine), for 2 reasons, there's a greater surface for algae that mbuna will eventually be eating and you can make bigger caves with larger rounder rocks, you can also stack them as high as you want, pretty much to the surface if you have enough lava rock.

If the slate is setup right it can be just as good as lava rock. Smoother 'carved' rocks (with the holes in them) are as good but less likely to cause any scrapes.

They are usualy about the same price. Problem with lava is there really isnt much extra surface area for algae, but the surface is much rougher than what they would be grazing on in the wild, so their mouths are not tough enough to be eating off such a rough rock.

You can buy slate tile in different sizes from Home Depot or Lowes fairly cheap...Then you can stack it as is or break it up to form caves and such. Here is a pic of a 29g my wife is cycling for a pair of Convicts.... Cost about $25 tax and all for the slate tiles...We bought 4" and 6" ones....Most place we have looked at want like $2 a lb for slate and ours weighed alot more than 12-13lbs. Plus these have smooth edges and we can restack them any which way we want too if we get tired of how they look.

For me it depends on the size of the tank. For smaller tanks i'd go with slate and for larger go with lava.