I have done a fair bit of research into this Steve and found that unless you pay big bucks for a photographic grade glass filter anything else you use will burn or shift its color due to the high heat. Good quality glass photographic filters will basically offset the money you will save by using a 6500 and trying to make it blue.
here is a quote from a guy on reefs.org that tried it using 175W mh's.
<blockquote><font size="1" face="Verdana, Helvetica, sans-serif">quote:</font><hr> I've done it. Used ROSCO theatre lighting gel acetate filters.
End diagnosis: it's not worth it. Just spend the money on some good 10K Ushio's.
Reason: The filter gels bleach after a while. On my 175W 4300K Venture bulb the gels only lasted 3 months before I noticed a significant colour change in the gel. The light output is sevelely attenuated. My mind kept telling me to buy a proper bulb.
After I listened to myself I bought a proper bulb and I was thrilled with the results.
I'll never use the filter gel method again.
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IMO spend the cash to get what works with regards to MH bulbs. Going cheap will only end up costing you more in the long run and possibly harm any corals you may decide to put in your tank. Do it right the first time and you will be much happier.
[ 19 February 2002: Message edited by: DJ88 ]</p>