Brad I think if i were going to have a hood with fans on it and over a 6 foot tank i would go with 1 on each end blowing inwards across the water and then 3 or 4 on the top blowing outwards to vent the hot humid air (assuming you cant run ducts). You could incorporate them into a controller as i do or just run them during the day on a timer with the lights or whatever.
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