Epiphany

I'm wondering if my fungal issues are actually stemming from the rain barrel? It's transparent enough to let in light allowing a mucky growth to form at the bottom. When I bought it I didn't think that it would be an issue because it didn't look like it would allow light to penetrate. Now however it's definitely the case. I've refilled the barrel with misted hose water to help disperse the chlorine and added a 1/4 cup of baking soda. I'll have to test a small portion of some plant tomorrow morning to see how it reacts to the rainbarrel/soda water. I'm hoping it's enough soda to help kill (or control) the fungus that may or may not be in the water but not enough to bother the plants. My only concern is if it lowers ph how will my acid loving plants react. Does anyone know if that's what baking soda does?