Quarantine tank - Water turned cloudy with a green tint

Over the last several days the water in my quarantine tank has turned very cloudy with a definite green tint to it.  Looking for ideas on what might be causing this.  Here's the background:
The quarantine tank (10 g) has been running continuously for at least 3 years.  I keep it running with two damsel fish.  It has an AquaClear filter, heater, and 15w flourescent light.  I always quarantine new fish before putting into the main tank.  Depending on the new fish, and how it gets along with the damsel fish, I have a divider that I can put in the tank to keep the new fish separate.
Water parameters:
Ammonia - 0
Nitrates - 0-5
Phosphate - 0
SG - 1.025
Temp - 78
Ph - 8.0-8.2
Alk - 3.0
Usually I perform a 10% change monthly.  With the onset of the cloudy water, I performed a 20% change about 5 days ago - and another 30% yesterday.  Hasn't helped much.
I've had no new fish to add to the display tank in a long time.  But, my royal gramma wasn't doing well in the display tank (it had been hiding for at least a week), so I moved it to the quarantine tank around the middle of Feb.  I didn't think that it was going to survive.  I dosed the tank with Melafix for a week (following the instructions), and the fish survived.  I also did a 20% water change at the end of the Melafix treatment.  About 2 weeks ago, I thought the fish might be better so I moved it back to the main tank.  Mistake.  It wasn't and it was getting picked on again.  So, two days later I moved it back to the quarantine tank.  I decided to move the damsel fish to the display tank, since the aquarium divider was starting to get algae.  So, the royal gramma is alone in the quarantine tank.
Oh, I had removed the carbon while I was using the Melafix.  I just put it back a few days ago, thinking that that would help clear up the cloudiness.  But, obviously it hasn't.  I wouldn't think that would be the problem, but the water has definitely gotten a more green cast since then.  But I don't have any substantial algae growth - just a little on the heater.
The only other thought I have is that the light bulb is way old......  Probably at least 1 1/2 years.  I've got a new one ordered from DFS.  Should be hear next week.
Any ideas anyone??????????
I was just ready to purchase a new fish.  Even though the water parameters don't indicate a problem, I'm thinking that it would not be good to put it in this water.