Ushio 20K I believe....

An XM 20k should also be fine.

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I don't really feel like taking the balast apart to see if it is pulse or probe. I also don't feel like paying for Radiums, though they are the best 20K I think.

If XM 20K's are good bulbs I think I'll try one, after all they are very reasonably priced, as said before.

There's no markings on the outside to indicate what ANSI rating the ballast is?

My guess is, you'd probably know if it was a pulse-start, they tend to be a tiny bit more cost-wise, so if it wasn't advertised as such when you bought it, it's probably a probe start.

Seems to me that every so often there's a sale on Radiums, that's basically the time to pick them up. I haven't really followed the prices of 400W lamps in the last few years since I haven't been using them. In the meantime try the XM's maybe. I *was* just about to suggest looking into the Venture bulbs, but never mind - I see they're about the same price as the Radiums nowadays (what the heck is up with that? There was a time they were *way* less expensive than the other lamps! I tried some Venture 250's last year coming off my Iwasaki's but coming off the Iwasaki's they were *way* too blue .. it like a discotheque in the basement kind of blue so to avoid culture shock I asked to exchange them for some XM's 10's instead).

Ushio 20k's are super blue.. a good blue though. Brings out tons of colour in your corals.

Mind you, I only used the 150w HQI bulb...

I just replaced my 400w radiums with XM 10k, so far the look is nice. We'll see how they burn in and affect the corals, I'll post a bit down the road with an update.
The 9 month old radiums are going to the curb, but if anyone local wants them for testing and demonstration purposes, let me know...

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Any chance you have before and after pics Brad?

I have before pics, so I can take a new shot and post it once I've run them for a week

one thing to note, if you are talking probe and pulse start a probe ballast will not start a pulse bulb, but a pulse ballast will start either.

also a thing to not usaly a pulse start ballast is only 15 bucks or so more than a probe type, by spending the extra money one a pulse start ballastt you will extend your usefull bulb life as it is kinder to the bulb with this method of starting.

so spend the extra couple bucks and get a pulse start. (Oh and for thoes that might wonder an HQI ballast is a pulse start type also. a little more bucks again but the best bang for your tank out of the 3)

Steve

Yup... you can run anything on an HQI ballast...