OK, I am almost positive that the Coralife mogul fixtures use probe start ballasts and the coralife mogul bulbs are probe start. A probe start bulb has a built in ignitor in the bulb itself. The Pulse start bulbs, which most of the high quality 250 watt mogul bulbs are, rely on the ignitor in the magentic ballast. So a probe start ballast may fire a pulse start bulb when it is newer but it probably wont when the bulbs gets some use on it. Plus it will underdrive the bulb, often by a larger margin,
So the bottom line is that you really need to replace the coralife bulbs with another probe start type of bulb. That leaves the radium out. I believe that Hamilton has some probe start bulbs in 250 watt but not positive. There are some options, you just have to make sure the bulbs are probe start. Probe start is older technology. I believe that the Hamilton bulbs may be probe start, the XM's are I believe, the coralvue bulbs including reeflux are probe start eventhough Coralvue recommends electronic ballasts or pulse start. I think even the Ushio 10K is a probe start (not the 14 or 20K). I think that most of the cheap 250 watt mogul base bulbs on ebay are probe start as well.
But all this assumes alot. It's from my memory which isnt always the best. If you can find an ANSI code on the ballast, it would tell your for sure whether it is probe start. M58 would be the code for probe start ballast. So basically, find a bulb specd for M58 ballast.
Your other option is to get rid of the stock ballasts and wire the sockets up with electronic ballasts if you are handy at all with wiring. That would allow you to use any 250 watt bulb. The ballast are anywhere from 70 bucks to 150 bucks or more depending on brand.
Personally, thats what I would do but Im kinda handy with wiring.
Otherwise, again assuming that it is a probe start ballast and Im pretty sure it is, you do have some options. You just have to be selective.
