I've had the CSS 125 and 220 on seperate tanks. It took about 2 1/2 weeks for the 125 to get broken in, and I tried any kind of mods I could think of. Finally just had to wait for it to go through the break in period. On the 220, I set it at the level it recommended for the break in period, and after about 2 or 3 days, it was broke in and no microbubbles at all. The white sponges in the bottom of the bubble diffuser box does get dirty and clogged. I just replace them when they got dirty with the cut to fit filter pad. One or two layers of it. One took two layers and the other took one layer to get no microbubbles. I also found that when the sponges/filter pad get clogged, then the water will start coming over the top of the diffuser box, and that would also cause a few bubbles. But once they both got broken in, they do a really good job, and both were without any modifications.