What Is It, How To Rid And Prevent It?

This algae is on the older leaves of just one plant. Very minimal outbreaks anywhere else in the tank.
 
I was just going to cut off the leaves with the algae, but didn't want to discard healthy leaves if I could help it.
 
Anyone know what it is and why its there. Also how to get rid of it and prevent it.
 
Stats are Amonia 0, Nitrite 0, Nitrate 10-20ppm, PH 7.
Weekly 20% water change
250 Litre
3 x 39W T5 bulbs. on for 6 hours/day
Planting is all low maintenance. No CO2
Airstone running 24hrs.
Powerhead circulating water
40 assorted small community fish
No issues with any other kinds of algae

looks like black beard algae to me.. there is a whole section on it here in the correct section on the forum.

I tried flourish excel , double dose daily for a week. Did the trick

when my plants get that i was told to put  the leaves and stems in but not the roots in a mix of one part bleach to nineteen parts water for two minutes and then after that let the plants soak in clean water before returning them to the tank.

Use excel first, thats the preferred method, double dosing and lower lighting to reduce the algae chance of survival 

To me it looks like Brush Algae. This is usually caused by high Phosphate and/or Nitrate. Another cause can be worn out Fluorescent tubes.

The tank is only a year old, and the tubes came with it. 3 x 39W. I have been thinking about changing them because I'm not that keen on the colour (slightly yellow). The offending algae is beginning to return a month after it was eradicated, although only very very small amounts. I have wondered if I maybe shouldn't have been using fertilizer?