Freshwater aquarium plants

Question
QUESTION: We have an 80 gallon tropical tank and are enjoying live plants for the first time. Things were great and then the plants started dying - or, really, melting - and I'm at a loss. I siphon gravel, check water quality, clip dying leaves, and I have even taken the plants out and rinsed off any slimy parts. I used a fertilizer 1 1/2 weeks ago and there has been no improvement. I really enjoy the live plants and would like to keep them, but don't want to keep sinking money into a "black hole." Any ideas?

ANSWER: Sounds like a lighting problem.

What kind of lighting do you have and how powerful is it?
What kind of plants do you have?

---------- FOLLOW-UP ----------

QUESTION: We have a full spectrum florescent tube and the tank is next to a western exposure window. The light stays on from around 8 AM til midnight. I wouldn't have suspected a lighting problem because the plants initially did so well. Could the tube be failing and we not see any signs (such as blinking, slow turn-on, etc.)?

We have some sword-leaf plants that have light green leaves with white outlines, bamboo in a plastic basket (it seems to be doing very well) and some other plants that I haven't been able to identify. They came from dried bulbs purchased in a package - kind of a treasure hunt! One has curly medium green leaves and shoots long stems to the water surface where a white long bloom occurs. I think it is an aponogeton ulvaceus. This plant had an offshoot that has not grown very much. And the last plant appears to be an Amazon swordplant. It has algae-like spots of dark green all over it. I had one plant that had dark green leaves with burgundy/purple undersides. It was a terrific plant for fry to hide in. It just melted when I touched it. The whole plant disintegrated.

Someone suggested I remove the plants and put them in some tank water in the sunshine with extra fertilizer to see if they recover. I'd love your further opinion.

Thanks.

Answer
Ok...but what I need to know most is the wattage of the bulb.

Either way, I can identify the main problem right now. You have your lights on MUCH too long. 16 hours a day!

Your lights should be on, depending on the wattage, 8-12 hours a day. I keep all my lights on about 10 hours a day. Anything more than 12 is crazy, no matter what strength lights you have.

So that's the first thing I would do. Do it slowly though. Turn it down maybe 45 minutes a day until it is at the disired length of time.

-Nick