That stuff CAN cause issues if it gets thick enough......I didn't have algae problems with hydroton but I don't use it anymore.

For algae there are a couple things you can do.....either cover your medium to block the light (you can use a plastic plate turned upside down and cut in half OR add hydrogen peroxide at 2 teaspoons per gallon every other day. Using H202 carries its own issues so look into it first.....it's much easier to cover the medium but make sure you allow for air flow and breathing room between your cover and the medium and drip rings.

PS...There is no such thing as too much oxygen in your solution.