About a week ago I noticed the gravel was turning a dark green color, and I saw green spots on the tank. I dumped the gravel in a cup and rinsed it out until it was clean, and I used a clean toothbrush to scrub the algae off the glass. For good measures, I also did a water change. It's been a week, and the algae is growing back! What could be causing this and how can I stop it? I have a 10 gallon, but I am currently bugging my parents to get a larger tank. I have one Hifin platy, two green lantern platy, and one Marigold wag swordtail.