Good post andyboy, I was about to state the same thing. A hps bulb needs an ignitor, the mh doesn't.
If the ballast was sold as a switchable one, then either there's a switch on it, or you have to open it up and route the wiring through the ignitor. Most electronic ballasts will automatically switch the ignitor depending on what type of bulb is being used. If the wiring already goes through the ignitor then you need a new ignitor.
It says a lot for the caliber of people who work in hydro shops that they didn't tell you this.

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Originally Posted by ceestyle
Don't be a martyr wasting $100 or more on CFLs to prove they're inferior for flowering pot.