Foam In Reservoir

I am actually growing in soil, but thought the problem might be experienced here more.

I have 32 gallon water reservoir next to my pots for convenient watering. The reservoir was filled with water from my garden hose and no chemicals were added to the water. However, I added an air-stone and a day later noticed a small amount of foam on the air-stone tubing and a little on the outside perimeter of the reservoir.

Is the foam something to worry about? What is it?

well, i've been using compost tea with an air stone in my res, and my res also has a submergible pump that constantly circulates the water,came the first time i tried it i tripped out, it had a nice thick layer of foam on the top, i've been reading about it, and actually watched a youtube video where some one was saying it's a good thing.. still want to learn more about it though