First sign of green algae in my tank

[Knight~Ryder]

It seems green algae has started appearing in my tank. It is appearing on one of the rock decorations I have. It doesnt seem the oto likes to go near it.

Why is it forming now and is it harmful to have in a freshwater tank?

[datchison]

I had that on my tank before but it was under the light just above the water. I did a NitrAte test and it was 80ppm for me so I did a water change. I think I was over feeding and the waste built up and caused the spike.

Could be because your over feeding and you think its gone because the fish search for food but I am sure it is not all gone and then rots in there.

I usually do a water change once a week or every 2 weeks now, I used to wait a month but that was to long for me. I do a gravel cleaning once a month.

[datchison]

I found this for you bro:

What causes algae (green water) in my fish tank?
Green cloudy water and algae growth can be caused by a number of things. The most common causes are:

A) Food: Poor quality foods are often high in phosphates and not very digestible. The waste produced then feeds your algae.

B) Light: Direct sunlight, a cool white household tube instead of an aquarium tube or the light being on for too long, can cause major algae growth. A household tube gives a different colour spectrum that will promote algae growth in your tank. A light left on for more than 10 hours per day will also make your tank go green or light from a window/skylight will also cause problems. Choose a position for your tank away from a window, use a good quality aquarium tube and set it to a timer for 8-10 hrs a day. Change your tube at least every 12 months blown or not, feed good quality food and use a gravel siphon when changing your water. These simple steps will help keep your tank looking great.

3) How often should I do a water change?
Tanks need small water changes often. Use a gravel siphon so that you are removing the waste from the bottom rather than taking the clean water from the top. Aim to change 10% weekly. Please age the new water in buckets with neutralizer and salts for at least twenty minutes, before adding them to your tank. Also, remember to get the right advice regarding what is a suitable filter for your situation.

[TheOldSalt]

Well, I guess that datchison already beat me to it.
It's not harmful at all, though, being only unsightly. In fact, it's actually quite beneficial. Too bad it doesn't look good. The saltwater guys have developed the ecosystem filter method for growing mass quantities of algae in a separate chamber out of sight in order to get the benefits without the downside, but this hasn't yet caught on in the freshwater arena.
For now, your best bet is to identify the cause and eliminate it.

[Knight~Ryder]

Well, I have been feeding more blood worms and mysis shrimp. That might be the cause...
oh and as far as the nitrate issure goes, mine was between 10 and 20 ppm