The kelvin (such as 6500K or 10,000K etc) is the measurement of colour as perceived by us (humans). It has no bearing on the light intensity (brightness) as perceived by the fish and plants. The higher K light may appear "brighter" to us because it is a cooler or crisper white light, as opposed to a warm white (4000K or 5000K etc) which tends to be "softer" in appearance. But all this has nothing to do with the intensity of the actual light, as measured in lumens.
You don't indicate the tank size, so I can't say much about your light setup, but I would think along with onefish2fish that cutting back to one tube might be necessary. Without live plants, light has only one function, to illuminate the aquarium for the aquarist to enjoy the fish. And this should always be the least amount of light necessary to do this. I explain the effects of light on fish here: Lighting: How It Affects Freshwater Fish
The light colour obviously impacts how the colours of the fish and other objects in the aquarium appear. Again without live plants, this is up to your individual taste. Personally, I would avoid excess in either direction (warm or cool) since these will distort the colours and not provide a true rendition. I find the colours of most freshwater fish to be sufficiently varied that having a basic "daylight" light providing a truer rendition of the colour is best. This also happens to be pertinent should you decide on live plants. Tubes with a K between 5000K to 7000K serve this purpose, with those closer to 5000K being warmer or softer than those closer to 700K. Mid-day sunlight is around 6000K I believe.
Any light in the absence of live plants will cause algae. That is not a bad thing, as algae serves the same purpose as live plants, consuming organic nutrients and CO2 and producing oxygen. And any type of normal algae is up to the aquarist. Algae is only "bad" in planted tanks when it attaches to plant leaves and suffocates the leaf and then the plant. So if you are thinking of live plants in the future--which is a very good idea in any freshwater aquarium--you should plan accordingly if you decide to change fixtures. I won't go further into this now.