Originally Posted by langod
So do you think the nutrient imbalance is caused by too much feeding? The water is crystal clear.
I have two full-length florescents now. (actually two individual single tube fixtures)
As I said above, one is a GE natural daylight and one is All-Glass Aquarium "Aquarium light" (kind of purple-ish compared to the other light, so probably more of a spread-spectrum bulb.)
What K (color) rating bulbs would you recommend for this tank?
First, "clear" water and "clean" water is not the same thing. Water can be clear but be a toxic soup killing off fish. And similarly the water may be cloudy but be very clean and of no consequence to the fish. Your filtration handles the "clear" part as it removes particulate matter. It should also help (along with bacteria) in the "clean" part. Just worth remembering there is a distinction.
As for tubes, since you have no live plants it makes little difference; choose what you like to look at, remembering that various tubes will give various colour hues to the tank. For a natural fish colour appearance, full spectrum is best, as it replicates the sun at mid-day. Warm white tubes will create more of a reddish or "warm" look, while cool white results in a bluer "cooler" look. Your natural daylight is full spectrum. The All Glass is purplish, as it is high in red and blue but no green to speak of.
45 watts over a 65 gallon tank is not excessive, but as you have no live plants you could reduce the light and the fish would thank you. Fish do not need light at all, the daylight in the room or the night-time lights in the room would suit them fine. It is only to view the aquarium that you need a tank light (unless you had plants which you don't). I would run only the one tube, the daylight, and see how it looks. You may find the fish are calmer and more colourful. Most come from dimly-lit streams with dark substrates and in such an environment can be quite stunningly brilliant in colouration. Also perhaps reduce the light period; 14 hours with no live plants is a lot of light, and algae will use it with the nutrients (from ammonia produced by the fish, fishfood, fish waste, bacterial processes, etc) to grow.
Which brings me to the brown algae. From your photos I am not sure this is diatoms, or normal brown algae. But whatever it is, reducing the light will probably have an impact.
Lastly, live plants; with your light you could easily grow plants like swords, Java Fern, Anubias, crypts, not to mention floating plants that being fast growers consume nutrients and use the light rapidly. In planted tanks algae is always at a disadvantage because the plants are better adapted to use the nutrients in the presence of light. And of course, plants keep aquaria healthier than any filter. Nature does it best.