Not sure - are the leaves all a nice healthy deep green, is so maybe you're overfertilizing with too much nitrogen. If the leaves are yellowish, then there might be a lighting problem. Other people on recent threads are having very good results with the Phillips colormaster 400w lamp that runs on an HPS ballast, and puts out a spectrum very similar to pure sunlight. I don't really go for the combo lights because I think there is a compromise in the reflector design; I prefer each lamp to have its own reflector, especially the adjust a wing now available on ebay, a lumen max reflector, or a reflectorized HPS lamp from HTG supply. For growing under metal halide, get a pulse start ballast kit from businesslights.com and use a pulse start metal halide. These lamps have a tiny chance of shattering so try to get one rated for a open fixture, but I've been using lamps with a closed fixture rating with absolutely no problems - the pulse start lamp is much much safer in this regard, compared to a probe start. Sativa.

The leaves were all healthy and perfect. It's just they were huge! Wider and longer. I'll probably get a HPS light to use this fall. Thanks for the info. I've had so much fun growing tomatoes and perennials under these lights. Right now I have roses under them just to see how well they grow. So far so good. They are blooming again!

Are you using a "generic" metal halide, or is it being sold as "horticultural"?, and what is the color temperature? Sativa.

It was a GE light that came with the ballast. Should I get one of the expensive grow lights? I'll look tonight and see what the temperature is. I know they have grow lights that cost 60-100 dollars, but I haven no idea if they are required. Are they?

No they aren't, grow lights are just regular lights in a different colored box. If I were setting up a new system, I would go with Phillips colormaster CMH which runs on HPS, but since you already have MH, I would consider buying an HPS ballast kit, because they're only about 50$ from business lights . com, you would use your existing cabinets, cable, etc., but you'd have a much more effective grow light. Throw out the innards, and replace them with the HPS kit. CMH is not marketed as a grow light, so it only costs about $53, its spectral output is just like the sun, with huge amounts of red light, blue light and violet light in the spectrum, and with that ballast you could even run a real HPS for maximizing your yields when the plants are in the flowering fruiting phase. Alternatively, pulse start halide is also a consideration, newer technology, more light per watt, but harder to find the ballast for the home gardener. Sativa.