it never ends
Does anybody know what the differences is between High Pressure Sodium lighting and Metal Halide?
I don't think just matching the wattage would work.There are some ballasts that can be used for both. Most are older cap and coil type ballasts though not the newer electronic type we see today.
You need to match the wattage of the ballast to the bulb wattage so unless you have some 1000 watt MH bulbs picked out I would look elsewhere.
I understand this I use 400watt 20k XM's on my tank and I wouldn't change it for nothing. Where I got lost with the guy using HPS @ 1000watts IMO would be very ugly color wise. Part of my light cycle I have two 24watt 10k T5's kick on about an hour before my MH come on and it looks dull and yellowish. And that's at 10k anything lower Kelvin wise is color I wouldn't want to have. The only reason I use the T5 10k is because it's a growth bulb.Generally High Pressure Sodium bulbs will be in the yellow/red range, as low as 2000k in color. Metal Halide bulbs used in aquaium applications generally start out in the 6500k color range which require copious amounts of actinic supplementation then on to 10,000k which is still very yellow but starting to appear white, to 12,000-15,000k which can start to be on their own with more of the blue white we are used to see up through 20,000k which can appear very blue.
HPS and even the lower k MH bulbs make it look like someone peed in your tank, very yellow and downright ugly. I used 2x250w 10,000k MH for several years and supplemented them with 2x140w VHO super actinics to get nice coloration. The growth with 10k K bulbs like Ushio and XM is fantastic as the PAR is very high, the trade off is having to supplement actinic. I am now using 12,000 k Reeflux bulbs with no supplementation and the color is pretty good. I plan to try 15,000 next change to get a bit more pop out of the corals but the trade off will be slower growth.
Ushio and Iwasaki make bulbs that can be used in either ballast but they are more for hydroponics and greenhouses and still very low on the k or Kelvin scale so would be yellow/red in color.
If you think about it if are suppose to be keeping things a close to nature as possible. When it comes down to it it's mostly the guy who is tying to sell you something is the one telling what won't work and what will.Way back when some of us first got started in reef tanks, myself the late 70's early 80's, we didn't have many bulb choices. My first bulbs were 6500k Ushios with normal output fluorescent Philips actinics for supplementation. The color of the Ushios and Iwasakis was really ugly but the growth was great. You look back on all the things you experimented with over the years and its a wonder some of it worked at all! I kept fantastic corals in a 20G high with only 4 normal output 18" fluorescent bulbs (two Vitalites and two Philips actinics) in the plastic undercounter type kitchen fixtures, no reflectors at all. I had monti caps and digitata growing like crazy along with a sebae anemone I still have to this day, 20 years later. People would cringe if you tried that today! And to top it off I used a modified Skilter 250 for both skimming and filtration with an old style Rio to boot. The Rio was later replaced with a Powersweep which was a real PITA. When I went from the NO fluorescents to 2x55w PCs the corals really woke up. Then the 150w MH was even better.....