[hoppycalif]

There is no ideal height above the water for a light fixture. It depends on the wattage and type of bulbs/reflectors, and on how willing you are to have light spillage. Assuming there is no glass or acrylic on top of the tank, I think the light bulbs should be about 2" minimum above the water, to avoid any possible moisture problems with the electrical stuff. And, with 26 watts of AH Supply type light, you can't go much higher and still have enough light to grow most plants. A ten gallon tank needs more than the conventional 2+ watts per gallon.

 

[hoppycalif]

Using 36 watts would be more likely to be satisfactory to you, and since the fixture is to be hanging, if you find it is too much light you can always raise it a bit.

The reason it takes more watts of light per gallon to get an adequate intensity for a 10 gallon tank is.......uh.......(my teleprompter is down, sorry.)

Seriously, I don't know why.