Metal halides aren't always simple. Keeping temps in check and the additional electrical draw have to be considered. But you have to consider that on a case by case basis. If you keep your house in the mid-70's in summer, have good ventilation or a open topped tank, and keep other heat sources in check(use efficient pumps)... Then it's really not bad. You also have to allow warmer temps in the tank. With LED or T5's, I could keep the tank steady at 78(3 degrees above room temp). With metal halide, the tank would peak at 82 in the summer(7 degrees above room temp). The corals didn't seem to mind. I did bump up the heater a bit, so that night time temps were closer in line with the peak. This obviously adds additional electrical usage. But if you are trying to save energy, you're not looking at metal halides anyway.
A little back story. I ran the same 180 gallon tank in two different houses, under several different light sources over the last decade. I started off with metal halides:
Then I decided to run a T5 fixture for a while:
Eventually I was excited to do LED's:
I didn't like the harsh shadows, so I added a BuildMyLED strip to help as an angled uniform light source. That helped. Coloration in corals was good, but growth was mild.
Eventually, I had some LED ballast issues during a really busy time in my life. The LED fixture used the same ceiling mounts as my metal halide fixture. While I sorted out what to do and balanced a heavy work load at the office, I strung up my old halide fixture as a stop gap till I had more time.... And then I forgot about it for a few months. Eventually, work settled down and I started paying attention to my tank again... And holy cow! I had some pruning and weeding to do. It was like someone threw coral steroids in my tank.
So I decided to leave the metal halides on. I did get new ballasts for the LED. Anyway, none of this is surprising really. Regardless, I had decent growth and decent colors with T5, LED, and MH.
Now I should mention, I haven't used the newest LED's and my T5 fixture was not top of the line. But my conclusion is this. Halides grow corals the fastest and have the potential for great coloration, but at the price of heat and electricity. T5's have good growth and great coloration in corals(sometimes better than mh), but I personally find the lighting to feel stale. I think that's a combo of no glimmer lines and the spectrum is weird to me(no matter what the bulb combo). And finally LED's are tricky. I personally feel par numbers on a 2'x2' square DO NOT tell the whole story. A reef is 3 dimensional! Most LED's have harsh shadows that impact growth and recession. I personally believe you have to use way more modules/fixtures than suggested by the manufacturers. For example, on my 180, I would have done 6 radions. I would definitely have to reduce the intensity of each module, but the multiple fixtures would have provided better spread and reduced shadows. That's just my opinion. And if you are running 6 radions versus 3 250-watt halides, the electrical usage might be a wash. But temperature would be easier to manage, and the controllability would be really cool with the radions! Unfortunately, that's just out of my budget for the moment.
So now, I'm starting with a new tank. I'm going to go with metal halides initially. Mostly due to cost and I want to crank out some growth. I want to go back into LED's ultimately, but I've learned I would need to splurge for double the recommended fixture or supplement with T5's. So I wouldn't be surprised to be running a LED/T5 hybrid combo down the road, purely to keep tinkering. We'll see I guess.
Here's the tank shortly before teardown:
