I just ran my RO filter to make 30-gal in a rubbermaid last Sunday. But 3 days after running my wimpy little airstone through it, the pH is lower than normal freshwater (I think it was 6.0). At one time I had a power head in there with the venturi air tubing hooked up and the pH tested at least 7. So I think it makes a difference. I don't have an extra power head either because this is only an issue when I'm doing a water change (which is not often
) and then I use my extra PH in the mixing tank. When using the airstone, at least I weigh it down with something so the air has to travel the entire height of the trash barrel to make it to the surface. Of course a larger air pump would work much better, but I'm using one of the smallest kind there is, so it's no wonder it doesn't do that good a job. That's an upgrade for another day.