Winter into Spring Barrel Pond

Hey guys. I built a small whiskey barrel pond last year that was very successful and rewarding. My plants and tadpoles thrived and I even had a water snake show up! My question now is, do I need to change out the water for this coming spring? It has been sitting dormant for the past 3 months. I cleaned a ton of leaves from the bottom and have tried to keep it clean. It still gets rained in regularly and many of the underwater plants are still alive. It does have a ton of green fuzzy algae that clings to the walls and large rocks under the water that did not used to be there however. Is this algae good or do I need to clean it? Should I replace the water with my rain collector water before spring? Give me your best advice! How do I best prepare it for optimal life and success this coming spring?