[Delphinus]

In case it helps, here's a sort of general guideline that I used when I was setting up halides. It's just a general guidline you don't have to follow it rigidly if you have a particular plan or look you want to go for, but since we're talking about an empty canvas here, let's just get you started. For every 2' of tank you want one halide bulb. So a typical 4' tank, two bulbs. A 6' tank (e.g., 155 or 180), go with 3 bulbs. Use your depth of tank to determine your wattage. So if you're tank is less than 20" then 175W bulbs will work just fine. For 20"-24" go with 250W, and anything over 24" go with 400's. Of course, change this at will. If you're going with SPS you know you will want more light, so step up the wattage. If you're going with a fish only or something then feel free to step down the wattage.

Ok, now as to your plan. For the most part, just run a halide bulb on the ballast appropriate to its size. So, a 175W bulb runs on a 175W ballast, which has ANSI designation "M57." So if a ballast is labelled M57, it runs a 175W bulb. M58 is 250W. Not to overly confuse matters but there is also a 150W halide size some people run, and these have their own ballasts too. Going into double-ended bulbs is a whole different story, and each of those has their own ballast, too.

But ... the bottom line is, if we're looking at something for less than $100 then odds are it is just a standard "core and coil" type ballast. All you will need know is the wattage. If it's 175W, then it will run any 175W bulb. The only real exception to this rule is when you get into electronic ballasts, then sometimes they are indeed tuned to a specific brand of bulb. But don't worry, for under $100 Canadian, we're not talking about electronic ballasts. They tend to be a lot more money.

I guess the only other exception is the Iwsaki bulbs, like Troy mentioned. These are mercury vapour bulbs that can be run on metal halide ballasts. So if you have a MH ballast, don't worry, you can still use an Iwasaki bulb if that's the bulb you elect to use. The only thing to watch out for, is, Iwasaki's don't come in 175W. 150W, 250W, and 400W. So if this is the bulb you want to use, you might want to not use the 175W size. The flip side to this, though, is that not all people enjoy Iwasaki's. To be honest, I run both 175W 10000K bulbs, and 250W Iwasaki bulbs which are 6500K, and there is little difference to the eye. The 10000K's are slightly crisper white, but despite the lesser wattage I don't see an obvious difference in intensity. I'm rather happy with those bulbs. So, I guess what I'm trying to say is, it's not the end of the world if you end up using a 175W ballast.

I hope I haven't just confused you more. Getting back to your case, my bet is your guy wants to know the wattage to be sure he's giving you the right sized ballast. That's all. With the exception of Iwasaki's which are MV, what you have is a metal halide bulb and what you want is a metal halide ballast. (Ok, so technically speaking some people are running Radiums on sodium ballasts, but that's a whole other story, so if you're thinking about going with a Radium, disregard everything I've just said.) Generally speaking pick your wattage based on what you've got and what you want to do, and after that there's little else except to buy the bulbs and turn them on and enjoy. 8)