Is the diffuser going to be fed into the intake of a filter or will it be in "open water"? Reason I ask is because I had the same question. I've used a Fluval and a generic glass/ceramic model and both have fine but not very fine bubbles. It is situated below an HOB
filter intake. At that point I did not think bubble size did not matter as good amount of the bubbles would be trapped in the filter floss. I am toying with the idea of getting a higher end diffuser from GLA or up Aqua.
Regarding the the drop checker, IMO
the mouth size will not really affect accuracy but more so the time it takes to reflect the true amount of CO2
present. Big mouth = faster color change.
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