We just started running 400s over our 75G about 8 or 9 days ago...heh...I guess we'll find out soon enough! Personally, I think the chillers are worth their weight in gold. I'm not one for keeping the AC cranked in the summer, as I get cold easily (a true Southern gal) and keep the windows open during the day...except in maybe July and August. With the outside ambient temps being so funky this time of year though, we have both a heater and the chiller set so the temp in the display stays around 78.5 to 79 degrees consistantly. As a side note, so far I haven't noticed the chiller coming on any more frequently since we hung the 400s, but then again, it's winter! ;)

Wendy