I have a 10 gallon tank and I know that the wpg rule breaks down in tank 10 gallons and under. I have a light with 2x40 watt bulbs(6700k), is it better to go with 4 wpg or 8 wpg. I have done will with my 29 gallon and can control it at 4.5 wpg with no problem. I would like to go with the 8wpg but will it be too hard to control? thanks for you help.