Hi,
I think the bubble build up may have to do with the pH setting and the recirculation flow rate. If you set the pH too high, the media breaks down too quickly and it produces very fine media powder. The media powder will slow down the recirculation flow and allow excess CO2 to build up. I have found that ARM tends to break down to fine powder at a higher pH then the regular medias. With regular media, I usually use a pH of 6.5. With ARM, I usually use a pH of 6.7. ARM with 6.5 is not stable with my reactor and it causes CO2 to buildup. So, I would try either backing down the CO2 setting or put in a bigger pump to increase recirculation flow.
As for the up flow and down flow, I use up flow with no side effects. I get around the up flow side effects by running a second reactor chamber. The second reactor acts like a filter and prevents the most of the fine media from entering the tank.
- Victor.
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