A green slimey (algae I assume) overtook my fishtank. I removed all the fishes, ornaments and gravel, cleaned the plastic plants and wood and put everything back with new gravel. The tank has been running for 8 days and I ahve noticed that the green slime has almost covered the whole piece of wood and is starting to cover the gravel again in "patches". What could be the cause of this slime and how do I get rid of it and also prevent it from returning? I have a few small tetra's in the tank and a pleco, temp is 22 degrees celcius, light is on 24 hours a day.