Does light k effect fw fish only tank

wont hurt the fish in the least you'll be fine

Lower K wont increase algae. In fact, the higher the K (5000K to say, 8000K) the closer you get to natural sunlight. The algae produced in an aquarium has more to do with how long the tank is lit and at what intensity. Water quality also plays a big role. Softer light, 4000K-3500K, is going to give the tank a yellowish look making it appear to be growing algae.
If you are after a natural light in your tank, I would go with 5000K-6500K. If you are after a more subdued, black water look, go with a 3500K-4000K. If you want to get your fishes' colors to pop, use a multi-spectrum light that utilizes actinic light. A combo light could be more expensive, but gives you the best of both natural light and a blue addition that will make your fishes' colors almost glow.
Just my opinion.

The only direct effect the k temp will have on fish is that lower k will wash out blue fish and higher k will wash out orange fish.


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6500k is the standard spectrum for the sun at the equator. I use 6,700k t5's from Home depot for $10 a 2 pack, phillips brand. Work great. Lots of light you get algae,,,,sometimes, they need a food source, not just light, as long as its not in the water volume your fine. Your never going to go algae-less. Personally i kind of like it on rocks. Low light you run the risk of diatoms, especially if you use a silica sand substrate. Green or brown, choose your color? lol
Light wont effect your fish's health, but on the other hand some fish are more sensitive to light then others. All depends on your species.