Would it be crazy to use 400w metal halides on a 240L African tank??

Thats alot of power. 400w x3 is 1.2kw/hr, x $.085 per kWh, your going to spend a $1.60 for every 16 hours they are on in electricity. Your going to spend $48 a month just to have the lights on. And that isn't even a warm / or filtered tank yet.

Just a thought but I would try to go green in the lighting department unless you have live coral or plants that need it to grow. Florecent lighting has temps and color too, and it is a place you can go green, unlike a heater or filtration where you cant get an eco- and wallet friendly version.

Don't some African cichlids like algae? If you put even one of your MH's over the 240 you should get good algae growth for the fish to nibble on. With that kind of wattage you could also put some Anubias and Java ferns in the tank.

I think any kind of plant, including algae is going to love that light. You can always get an algae blocker. Personally, I get alot of algae, with my plant lights and iron and fertilizer supplements for my plants. I had africans with rocks and plants--I know they eat plants they are omnivors, I try to grow enough so they can graze, but that means extra lighting, iron, etc and along with that comes extra algae. I use two items that take care of my tank quickly 1st one of those 6" plastic scapers (they come in 8" and 12" too for big walls...um I mean tanks), from Home Depot wont scratch glass or acrylic and makes quick work of cleaning glass....2nd a stiff plastic bristle brush, like one you would use to clean your car rims, this one from Lowes though, takes algae right off rocks. Forget those gimics that they sell in the Pet shops, they dont work. Just run your items through a sanatise & water heat cycle in the dishwasher before useing the 1st time, and after use to clean (and always prime the diswasher by making sure the water runs hot out of the sink before starting it--this will improve any dishwashers efficiency 10fold) Use a cup of distilled vinagar instead of soap in the dishwasher. Distilled nagar will rinse and evaporate off leaving no toxic residue, heck if you wanted you could use distilled vinagar to pH down a tank with high ammonia levels after you, get some ammolock in there. I used to be afraid of algae, because it was so hard to get off, it was just too much work. Now I couldnt care less because it is so quick to using a huge scaper and huge scrub brush.

anubias and java fern would sustain and probably grow some under regular fluorescent lighting. Under halides, you'd better be doing some sort of nutrient supplementation (maybe just a ton of waste from the fish), or their growth patterns will be pretty messed up. under a 400w halide, you could keep pretty much any freshwater plant you wish, and 95% of all plants would need some serious acclimation to that kind of bright lighting. If you have mbuna, they might like that situation, as they live in the shallows of lake malawi (the same goes for the tropheus of tanganyika), but as far as peacocks go, they are from the murky, deeper waters, and only venture up into the shallows to prey upon fry of mbuna. This is a generalization, but a pretty accurate one. If you raise fluorescents high enough above the water such that it is pretty much just ambient light, you can get a shimmer. However, I'm with you on the halide shimmer.... SWEET. I foresee some major algae problems in your future, and probably some skittish fish too...